Inky, the smallest AND most dense stone layer dominates the overall color of the ground. So with that in mind, if you want a light brown overall look, just make sure the smallest and most dense layers have that color. The slightly bigger stones, but not the tallest ones, are where you are pretty much free to introduce any other natural stone color, grey, black, white, rose, yellow... without destroying the overall color. try it!
Cheers,
Frank