Just experiment. A good colour from stone is mostly gray, with only a tinge of maybe yellow, brown or green. Sometimes it can be tinged with blue, but that tends to create a very cold-looking stone and should probably only be used for themed packs.
For beginner artists: It is helpful, yes, but don't be afraid of trying something new! You can always copy people, but one of the best artists "evolve" from these kinds of knowledge, if that makes any sense. I guess what I'm trying to get across is you can always add your style, your little touch to art. That is what makes textures unique
Anyways, I'm glad you've made this post. Many people say how their textures are never any good, which pains me to see. Nobody start out amazing, we've all been terrible before.