More colors take up more space, so the number of colors was a major limit on early 8-bit graphics/games. I don't know what the actual limit is, though. Modern-day bitmap files run into the same problem, more colors make an exponentially bigger file. That's why we don't use .bmp for photos, it would take up ridiculous amounts of space.
Ah i c what you mean there! Well, I didn't export this picture as a .gif so I didn't see the color count Besides, 8-bit graphic was only an inspiration for the style, I dun think there is any color limitation for this contest la