Canterlot castle was as large as it was embellished. It was the face and heart of Equestria, where the diarchal princesses lived, where the military made its primary home at, and where most of country's trade ran through. If you were trotting through the halls of the castle, you either worked there or were being escorted. In this case, well, neither applied.
Snowball, after entering through a door (which had taken him a few second seconds to figure out), trotted through the halls undisturbed. The castle was something that amazed him. It was made out of rock (marble)! Every building he had ever seen, up until now, was either an igloo type building made out of snow or ice or a setup tent that was made of fur or cloth. Every building he had interacted with in his entire life had been temporary, only meant to be used for short periods of time before moving on within a week or so. So was the life of a constantly migrating pack of Yakutians.
He had every reason for somepony else to stop or bother him. He wore no uniform, was unescorted, and was a Yakutian, a subtype of pony that was essentially never in Equestria. Fortunately for Snowball, he would only be stopped or bothered if somepony actually spotted him. The insides of Canterlot Castle was as embellished as the outside was embellished. Every season, the inside was redecorated to match. This means, it was decorated to match the holiday. This translated to green and red trims decorated everything. The green and red trims were the secondary color used to decorate everything. The primary color was, you guessed it, white. The primary decision behind this was to save on the amount of work to decorate everything as the walls and floors were made of white marble.
Snowball, when he stood in front of the white walls, or on the white floors, was essentially invisible. However, somepony could obviously see him when he stood on any of the definitely-not-white rugs or in front of the definitely-not-white tapestries and curtains/decorations, such as a suit of armor. You'd have to specifically be on the lookout for somepony like Snowball.
Normally, anypony behind the walls of Canterlot castle wouldn't have to put much effort into noticing that somepony else was there. Whenever hooves trotted on the ancient marble floors of the castle, the resounding clop would reverberate through the halls, indicating that somepony was there. However, this case involved a Yakutian. Yakutians were the silent migrators of the north. Living way beyond the Crystal Empire, they spent most of their lives in snow. The north was a cruel and inhospitable field of white where you had to trot carefully as every careless step would result in a resounding crunch in a usually silent environment, signaling to any nearby predators where meals could be found.
Naturally, nopony noticed Snowball. That is, until the moment when he had decided to spent some of his attention towards a suit of armor. While Snowball's attention was diverted, he was left standing in the middle of a hallway on a spot in between floor rugs, where he near flawlessly blended in with the white marble he stood on. A female batpony maid, who was making her way through the halls by hovering, accidentally flew into Snowball. Crashing into Snowball was the best case scenario for anypony to accidentally fly-crash into due to the shear amount of fur that Snowball sported, it being a natural soft cushion.
The mare bounced off of him and landed on her flank, dazed from the interruption in her flying. Looking to where she had intended to go, she was confused as she seemingly had no obstacle that could have posed enough of a barrier to have had stopped her in such a manor. That was when she finally realized that somepony was in front of her when the pony in question blinked twice.
Snowball had thought about running from the mare, his past experiences with other mares in Equestria being rather negative, but this mare had something about her that roused his interest enough for him to bait him into standing there. She was wearing the most peculiar outfit that Snowball had seen. To anypony in Equestria, they'd recognize her as wearing a stereotypical maid outfit but to Snowball, he recognized nothing. It peaked his interest as clothing and fashion in general wasn't really something that Yakutians practiced. He tilted his head a few times in both directions, trying to take it all in.
Meanwhile, Snowball's meticulous screening had given the maid enough time to discern what/who she was dealing what. "Deepest apologies sir! I wasn't aware of your presence!" the batpony loudly apologized. She was hoping this wouldn't cause her much of a reprimand. Considering she was dealing with a stallion, she was dearly hoping that he wouldn't exaggerate the situation to any of the castle's higher authorities/supervisors. She gestured behind herself with a wing. "Day court will be ending soon for the holidays."
That was when she realized that the stallion in question was just here, by himself. He wasn't wearing anything like that of Canterlot's population. He was by himself so he obviously wasn't a visitor, being escorted by no one, nor was he a member of the castle's staff, having no uniform. The smallest inkling in her mind suggested that he was some sort of criminal element but was dashed away by the logic of him being a stallion and the fact that he hadn't bolted like anypony in such a career field.
That raised the question, what was he doing in this castle? His unique appearance, that of being a Yakutian with a beautful fluffy coat of snow white fur, further raised the inquiry. When Snowball gave no reply to her statement and continued to take in her appearance, the maid opened her mouth again. "Sir? Can I help you? I can take the responsibility of escorting you safely to where ever you need to go! It is my duty as a mare to make up for my mistake and to protect a stallion such as yourself!"
Snowball raised an eyebrow at such a statement but mentally shrugged and pulled out the same letter he had been showed to the family that he had met at the park. He showed the letter to the batpony in question who took the scroll in her wing and read it. When she read the contents of the letter, the once bluish grey batpony turned white. She had assaulted the diplomat of another nation! She had frozen up at the thought that her life was over. She would have been a good stand-in for one of the marble busts that decorated the castle considering the fact that she had turned white and made the same amount of movement as one of them. However, the sound of her heart beating loudly would have betrayed her true status of not being a marble statue. She wasn't ready to go to the dungeon! It would have been a lonely existence being locked up down there, though it wouldn't have made any difference to her romantic life considering her failed dating life this year, she truly hadn't been able to see Snowball standing in the middle of the hallway when she had been flying.
She returned letter back to Yakut's diplomat and mentally debated her options. She obviously had to stick with the diplomat and explain the situation when he would inevitably describe the incident and portray her as some sort of alley vagrant assaulting an innocent passerby. She had two options as to where to escort the Yakutian to. The, by far, worse option would be to take him to meet Prince Blueblood who was supposed to be the pony designated to entertain diplomats. The prince would blow the situation way out of proportions and her name would end up in the press before she could blink. The next solution, which would still result in her public death, was to take him to Princess Celestia. She was the alpha mare of Equestria, and possibly the world, but she was still fare... Hopefully.
She left her thoughts and turned her attention back to the Yakutian... She shattered into a billion pieces, or felt like she shattered into a billion pieces. He had disappeared. She had thought that she had lost track of him with how he blended in with the walls but after some searching, she realized that he was gone. Welp. She heard the dungeon jailers were nice this time of the year. She had frozen in the meantime, long enough that by the time she had been roused from her paralysis, other castle staff had gathered around her and had been trying to figure out why there was a mime dressed up as one of the castle's maids and performing amazingly in a random section of the castle's hallways with no apparent reason.