Charcoal epoxy with black sand--the "norm"
Charcoal epoxy with mixed black and white sand = light gray
Charcoal epoxy with white sand
Limestone epoxy with white sand (looks like coral beach sand)
Normally the surface of the epoxy is seeded with fine sand, which adds strength and helps protect the epoxy from ultraviolet light. Here are some of the combinations used at Blue Blazes Glass.
It is also possible to not use sand--not recommended for exterior use. See below for the look if this is covered with gold leaf.
There is a definite difference between white sand on charcoal epoxy versus limestone epoxy.
Gold leaf makes a big difference when the window is lit from the front, but is not noticeable when the sun is behind the window. Oscar Wilde on the left (from the Diamonds page); detail from the Diamond Heart Cross on the right (Crosses page).