Hey Chuck, that's looking pretty good...even if your rip-rap needs to be a bit more "angular"!
As for colors, on a mostly cloudless day in the middle of it in the desert, your hills would probably be a shade or two lighter than your foreground colors with a touch of purple/blue. Overhead, patchy clouds make that formula moot as Scottl's photo clearly shows. Generally, when painting landscape scenery, I make my distant land formations lighter and more purplish/blueish in color than my foreground...here's a sample...
Photo (1) - Showing Lighter Colored Background Hills Than Foreground Scenery:
The further away they are, the lighter and more purple-ish/blue-ish they are.
I even fade my unfinished 3-D Styrofoam hills to make 'em look further away.
Although "sky" color is highly subjective, I took paint chips into the parking lot at The Home Depot when selecting my sky color and compared them to the cloudless Utah Summer noon sky intending to fade it at the horizon. I fade the horizons on my skyboards by airbrushing a thinned, opaque whitish-blue until I get the effect I want. This mixture is what I fade my 3-D hills with too, and I'm planning on doing it even after I put finish ground cover on 'em.
Photo (2) - 3-D Unfinished Styrofoam hills at the West End of Echo to make 'em look more distant with darker blue skies faded with a "partly cloudy" appearance:
Anyway, your efforts are looking good and doing a "Practice Stretch" is an excellent way to see if your methods are going to work to your satisfaction. I highly recommend it.
Cheerio!
Bob Gilmore
