NcgOsh, welcome aboard...
for the most part the gravel is a dull beige white grey about 3/8" +- gravel from river beds. As riverbeds can no longer be mined other gravels are substituted.
If you try the search box in the upper right hand corner there are several entries that would apply to your question. Since I do not know the color of the stone you are using, I can not recommend a color.
sample thread with some additional information :http://japanesegardening.org/talk/index.php?topic=692.msg5591#msg5591
hope this helps, or please refine the question, edzard p.s. make sure the gravel does not glare and is a matt finish, pure white is not a good solution.