There are only 2 variants of sand available, red sand and sand. I think they should add all of the colors of sand, like: Yellow sand, Red sand, Blue sand, Gray sand, Black sand etc. These types of sand probably don't exist in the real world but this is minecraft! minecraft is fictional. Maybe to be even more fancy, maybe smelting the sand in a furnace gives you the same color of glass the sand was, for example: red sand gives red glass.