Materials for realistic landscaped stream beds?

When creating a mock stream bed in a landscape design, one suggestion is that you mix it up a bit. Natural river beds are made up of a variety of rock, sand, gravel and soil. We have seen a mixture of 4" to 6" river cobbles, 1 " to 2" cobbles, crushed rock and a sprinkling of field stone. Using soil in your mock stream may create a weed issue.

How do you mix materials to make your landscaped stream look realistic?

What colors do you expect to see in your streambed mixture?