I wrote this a while ago in the Art for Fanfiction group, crossposted it to 'Bad Art!' and thought I'd copy it over here, too. I'm not stickying it at the moment, as I'm planning on reworking the way tutorials are handled here a bit.

This was the initial post, then two replies I added on it later, but I might as well combine them here.

First of all, I just wanted to go over what this is and isn't for. This is how I color sketches in Clip Studio Paint.

Now, first off, this is how you color the sketch if you aren't planning on going over it and redoing all the line art electronically. It'll probably look pretty good if you just trace over all the lines in a new layer, and redo the linework how you want it and such. That'll also lose some of the roughness of the original, of course, and be slower. I can color things that way. But, you know, I kinda like how coloring pictures comes out this way, too.

If you are going to trace things, I'm gonna suggest using vector layers and the continuous curve tool, since this is Clip Studio Paint. You can get some really nice lines that way, and the vector layer means you can readjust the lines afterwards.

And, obviously, this is Clip Studio Paint, not Gimp, or any other art program. There is a way to convert brightness to opacity in Gimp. I looked it up. It was something like in the image mode, make sure the picture is RGB, under Layers in Transparency, choose "Add alpha layer", and then in the same menu, choose "Color to Alpha". Gimp is weird. And trying to draw in it with a graphics tablet really sucked when I tried it. Maybe the settings are messed up or something...

So, anyways, here I am in Clip Studio Paint with one of Grim Grin's pictures:

So, first off, we need the background to be totally white. Usually scanned images or ones you took a picture of have some degree of shadow on them. This one isn't too bad, but still, I'm going to go ahead and so a brightness/contrast filter layer.

You just basically play with the brightness and contrast until the background looks pretty white, while trying to keep the lines looking good, because the more you increase the brightness, the more they'll wash out. If this doesn't work out, there are other filters you could try. Tone Curve, for example.

I went with brightness/contrast here, though. Next, since it looks good, let's just merge down the filter layer.

Now, go to Edit and choose "Convert Brightness to Opacity".

This command is magic.

Now, lets insert a white paper layer. This'll just be a solid color layer at the bottom of your layers. It's just easier to work against white then squares.

At this point, zoom in several hundred percent, and look over the picture with an eraser in one hand and the undo command in your other. Erase anything you don't want that's in the sketch. Things like random dots or dust in the background, setup lines that are still faintly visible, places where a line was redone and the old one is still there, and such. You can also clean up the edges of lines that are looking rough, trim things, and such. Just make sure you don't erase too much.

Oh, since this is Clip Studio Paint, keep in mind that you can choose transparency as your color and erase with any paint tool. Erasing with the continuous curve tool can be really neat.

While we are thinking about it, let's set the layer with our sketch on it as a reference layer.

You see this "Do not exceed line of reference layer" option?

When it's checked, on a tool, that tool stops at all the lines of your reference layer. You'll probably be flipping this on and off, though, because you'll tend to get the color stopping shortly before the lines, due to aliased lines. I like to have it on the eraser tool, though.

Now, let's toss a layer right above the paper layer and start coloring!

Okay, yes, I colored over her eyes. I'm going to do a layer above this one with white on her eyes, and it's easier to see when painting white if there's a color below it. I'll do that and start the mane.

Stay within the lines. The lines are your friends!

Okay, actually, sometimes I like to just really sloppily color an area. Note that this layer is below the layer with her fur color, so that anywhere I overlapped there doesn't show. Next, though, I took an eraser and erased all the sloppy bits. I think erasing overflow is easier then trying to get it perfect the first time. (Especially with my eraser stopping at the reference lines!)

Also, just to mention, I separate my coloring onto lots of layers, so that anything I do on one doesn't affect anything else.

And, you know, I suppose I can do a bit of shading, though I'm not great at it. What I'll do is create a layer right above the layer I painted on, then click on the "Clip At Layer Below" icon. Now anything I draw on on that layer only appears if it's a spot I colored on the layer below! Yay, masking!

So I did that and stuck a dark green layer below everything for a minute, so I could see the little bits of bright color standing out that I need to erase easily.

Okay, enough of the green, I'm sticking a gradient layer above it.

I also colored in the eyes, which I'm not covering here, especially since I barely colored them this time, so it wouldn't be a great one to demonstrate on. (Pretty much, you paint the whites in, paint in the pupil black, you paint in the iris on one layer, stick a gradient on it with a clip layer, paint one or two lines on the side as highlights, again with a mask, and then paint some white glimmery bits on top. But i didn't really bother with all the steps here, because not much was going to show. There are multiple ways to do it, anyways. This was just show-type eyes.)

And I've got a feather brush that I used to stick some white feathers in the background, which got me to this point.

And that seems reasonable to me!

Anyways, not sure how much this helped people, and I'm sure there are people that color better than me, but I figure this'll give people that aren't sure where to start an idea, though admittedly, I went kinda Clip Studio Paint specific several times. Oh well, guess it shows some of the things I like about it, too.

If you have any questions, let me know, since i sort of slapped this together and haven't done much in the way of art tutorials. And if you have ways to do parts of this better, say that, too, since this is mostly how I do it, not the one true way. I may be painting the color in by a paint brush, but you could use a paint can, for example...

You know, I don't feel like doing screen shots right now, but lets talk a little more about the actual coloring bit of things.

As I said, there are multiple ways to do things. I just like doing things by pen. I'm gonna assume that you are coloring on a separate layer for just the part you are coloring at the moment, and that the linework is a reference layer, though most of this probably won't be too Clip Studio Paint specific.

First, I mentioned what I suppose you could call the slop and glop method. Grab a pen without the "do not exceed the line of the reference layer" option on, paint sloppily all over the thing, getting all the area you want, but not worrying about going over lines, and color. Then grab an eraser, probably with that option on, and erase all the bits that go over. This way, you are doing all the precision bits at once with the eraser.

There's an obvious inverse to that method. Paint all around the edges first, then color everything inside afterwards, either with a brush, or the continuous curve tool (or holding down shift to get straight lines with the pen). This can work pretty well too. It's a lot easier to color the bulk of stuff if you've already got the tricky bits. You could also use a paint bucket or such to fill in the rest.

Okay, lets talk about the paint bucket for a minute. There are reasons I don't like using it.

You probably used a nice fuzzy brush with antialiasing when you did the outside, didn't you? I tend to, and that's horrible for this. What you may very well end up with is a line that's not colored around all the edges of the part you used it on. You can then go and just paint that in, but it's kinda a pain. You can avoid this if you use a brush that isn't antialised. You could also play with the "color margin" and "close gap" settings. And remember that you can set whether it refers to all layers, the reference layer, or just the current layer. There's also a "paint unfilled area option, but I don't really know how well that works.

Other methods? Well, you might get some mileage out of the magic wand tool.

What you do is go to your linework layer, click in the area you want to color, and it magically selects the area. Hold down shift and click areas until the whole area you want to color is selected, as that'll add the selections together. Now go to your color layer. What you'll probably want to do next is go to selection and "Expand selected area", give it a few pixels, maybe 2 or 3, and eyeball things to see how close to the edge you are getting. Undo is your friend here, and there is a option for shrinking, too.

Once you have a good selection, you can just use the paint bucket set to only that layer, or there is a Fill option in the Edit menu (and an "Advanced Fill" option, thinking about it, but I haven't played with that). Deselect afterwards. Or you could just start painting with a paint brush in the selection, of course. You can use other selection tools for this as well, mind you.

Now, one thing to keep in mind with any of these is that you're not stuck with just what you colored. I mentioned before that you can just put a layer above your color layer, and clip it to the layer. You can do all sorts of things with this!

The obvious would be that you do shadow and highlight layers. Just stack them on top, and color in with lighter and darker colors. If you aren't using reference colors for this, make sure the darker version of your color and the lighter version aren't just the same color but darker or lighter. Change the hue a little to make it interesting, though not too much. This is very much an eyeballing thing.

You could also stick a gradient layer over it, clipped to the color layer, This can make for interesting effects. You probably want the shape on either circle or ellipse. Even if the dark and light colors are close, this can still make a noticable difference.

You could also just paint with the dark and light colors and play around with the blend and blur tools. I actually do this to fake gradients in eyes sometimes. Paint in a top dark eye color, a bottom light one, another shade in the middle, then blend along the lines. You might be surprised how good this can look sometimes, if enough detail is on top of it, and you make sure there isn't anything obvious showing through, like a line you didn't blend, this can look pretty good!

Anyways, that's probably enough for now. I just felt like talking about things you could do a bit more, and writing up these this is fun, and hopefully useful. Some of this might be obvious, but, you know, sometimes obvious things aren't. also, it doesn't seem like tutorials get posted here, much, and i think that's kinda a shame.

Not sure if anyone'll read this, mind, but hopefully they do, and it helps out...

Just thought I'd show you another way to color that crept into Clip Studio Paint within the last version or two.

Grab a piece of line art. Here's one I found on derpibooru by kryptchild.
https://derpibooru.org/108006

Set that as a reference layer and make a new layer. Scribble on colors a bit where you want them.

Go to Edit->Colorize->Use hint image and colorize. There's also an option for doing it without hints if you want to skip the section where you scribble, and an advanced one. Here's what using a hint image looked like.

While that's kinda light, I think it looks nice. The colors are all on a separate layer.

You might be wondering what it did without any hints. Well...

I think it's expecting humans more than ponies.

Advanced just mostly lets you fine tune things. This colorization option looks pretty fun to play with!

--Sweetie Belle