I've been away working and was shocked to come back and read the fun activity on this thread!
Back to the colored river rocks, Lin: buy some concrete paint, water it down, and create a wash over the ones in various colors. ALSO: Acrylic paints watered down a lot will do the same thing but may need refreshing every couple of years. When you paint the rocks, you want the paint to be very watery so the rocks own spots show through.
I think
@Trish made river rock feet a couple of years ago. Maybe three? Time flies.
Lin, I love the atrium too. I do love yellow houses though with black trim and a red front door.