Im not so sure about the dyed sand only because it could release chemicals. If your talking about the type of sand you see in those clear bottles where they make cool designs with then i'd say no. Alot of different aquarium companies make different types of sand, some colored and some not. The only colored sand i've ever seen though was black. Which isnt really a color to begin with. Its in your best interest to go with sand that is made for aquariums or to be under water because they dont have any chemicals added to them that could be released into the tank water. Something like play sand, and pool filter sand work great because.. its just sand. Although, pool filter sand is alot cleaner and nicer looking than the play sand. Also, the pool filter sand comes in some different colors depending on the outlet you get it from. My local pool store had Tan, white, and white with black specs.
Last i checked i dont think you can have that many plants in gravel, if any at that. Go into the gallery and i dont think i've seen one single picture of a planted tank with gravel. I could be wrong though.