As a Sexton in a church one of my duties was to dig the graves for for cremains to be interred. Having done 4 funerals I've seen 4 different people's remains. All were an off-white color and had a gravel type appearance with small pieces of what I assumed to be bone.
Are all cremains basically the same color, some form of white? If not, what would create a different color, perhaps a dark gray and partially pulverized and stuck to the plastic bag?

An intriguing question - I wonder why you ask?

My experience is limited to four internments involving cremated remains, and all were pretty much the same - greyish powder, finely ground. I know little about the commercial cremation process but do know that it involves pulverizing after cremation - otherwise you'd have big chunks of bone. Perhaps different funeral homes use different techniques or settings, so there is going to be variability in the granularity of the final remains. The ash is always very dry, so unless the plastic bag is punctured or opened to let moisture in I don't see how the ash remains would clump.

Both my parents were cremated, and the appearance was very dry grey powder mixed with some larger pieces and a few obvious slivers of bone.

I wonder if you encountered someone who was cremated in a real coffin rather than the state mandated minimum cardboard box or shroud. Each state has different laws. Or the bag was punctured, as ebaines suggested. Or the person was cremated with a favorite object.

Cremains are gray and white in color. Regards v Tom