Yellow. Sparkmans primary color is yellow and it would make sense for it to be yellow (lighting and all that) Maybe add some red to accentuate the yellow in certain areas. It does look a bit too similar to Flame Wingman though that's not the artists fault. There's nothing to really go off of either. My best bet would be to base it off of Fusions that already exist like Plasma Vice or Darkbright. As for the pose, I'd say maybe lower his non dragon hand and have him holding/casting a lighting ball or something. If you dont want to keep the pose then maybe something akin to Dark Laws pose or Shining Flare Wingmans pose. That's just my take on it. Art is pretty good though