No global guarantees, but most talus I've seen has a color component identical to the rock face that shed it.
Component, because there's usually other stuff in therre, like dirt, and sand, and if it's a live rock glacier, a moving stream of rock, you're seeing a lot fresher surfaces on the talus than on the long exposed cliff face.
I've tried gluing down the talus, then just painting it, and wasn't satisfied. Too uniform and it just looks funky. The best results so far, come from:
1. Paint the underlying surface.
2. While wet, sprinkle widely varying sized talus, scree and sand where it needs to go.
3. If need be, for thick deposits, glue it like you would ballast. If the sub-terrain is already carved to match the talus accumulation shape, then you can get by with as few as two layers of talus stuck on paint, saving expensive artificial talus.
4. The problem with the above method is that the wrong colored talus is on top of the paint. General paint looks iffy. So here, we use a small brush and dab paint on individual rocks or on small areas, leaving some unpainted and natural, so there's some variation in color, but there's also a good match between some talus and the rock face above.
Still not 100 percent satisfied, but of the methods tried so far, this is the best.
Vertical strokes with a very narrow brush, using thin washes but applied nearly dry, using as much color variation as your basic rock and soil colors allow, following the fall line down a bowl or down a talus slope, or down a meandering fall line in an avalanche chute, gives a good effect you often see on real talus slopes where the color variations are somewhat arranged along the fall lines.
Not the best pic, but you can see some of this here:
Mike:
I've experienced the same problem using Woodland Scenics talus. I've found that artist's acrylics diluted well with 50% isopropyl alcohol:water makes a good wash to tone down the talus' color. I prefer a wash of burnt umber followed by one with black. I've colored the talus both before application and after glueing in place with diluted white glue.
Joe