These are a number of individual small pieces put onto one large sheet for the sake of saving time uploading and to avoid spamming the gallery with a bunch of teeny-tiny pieces.  Because they were composed individually, they weren't made together with a unified palette, and that number is likely the composite count of all the pieces together.  Each individual pony is something like 12-16 colors, IIRC.  Maybe a few more for ever-colorful Rainbow Dash.

27 px tall apiece (The forum I was making these for had a 27 px height max), variable width.