This is probably a bit late, but I just noticed the original post and since I used to do the "Sands of the Desert" I felt I should throw in my three cents worth.
The use of a hand towel to dry one's hands between sand colors is a natural for another sort of color change. My towel would start white, and then when I produced the red sands, I would wipe my wet hands on the towel and it would turn red. It was also helpful in providing access to the loads, as you may imagine. Each time I wiped my hands, the towel changed color. I used red, yellow, blue and green, plus the original white and ending with black.
The loose sand was caught in a little transparent glass flower pot. At the end of the trick, I would flick the black towel at the four flower pots and each would have a small flowering plant in it, with flowers the color of the sand.
A few years back, sand paintings in glass bottles were the latest fad for arts and crafts. I always thought of making an ending where I would pluck the flowers and pour the sands into a large glass vase, only to have them swirl up into some kind of desert design, but the fad didn't last long enough... or I was getting too old... or something. I never did use that idea, but I offer it to anyone who can make it happen.