Use plain table salt & colored sidewalk chalk. Pour the salt into a shallow container, "rub" the chalk over it, before you know it you have colored "sand". My Girl Scouts loved doing this sand art craft.
Back when I was a kid, we did a similar project making colored salt. Using colored chalk, put a small amount on some paper and rub the salt with the side of the chalk. Continue rubbing the salt until it is the color you desire. Then we used the colored salt the same as you would use colored sand. I know its not sand but I would imagine you could try this with sand and see what happens.
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