Skeetendo

Hey im pretty much a noob in pokecrystal so sorry if I ask about a dumb question, I tried to look for tutorials on the matter but I didn't find any.
so my question is: how to add custom tiles to pokecrystal, I noticed that in the directory of the pokecrystal project there is several tiles but they are in monochrome color plus some attached files holding the same name of those tiles, I assume maybe those files give the color to those grey monochrome tiles, it's not really clear for me.
also im questioning if there is any limit for the ammount of tiles used in pokecrystal, as a side note Im using Polished Map by Rangi.