I like sand as well.
You could put your choice of gravel/sand down then use the gems as an accent. I think I saw a member here who had something like that in the "post your betta home" thread. It was really nice. I think she had 3 gems in the middle of her tank, all of the same color. It was nice.
In my 55 gallon I had black gravel down, and I used large aquarium safe "dragons eyes" or something like that. Basically, large round red marbles. I also used some clear ones, it looked really nice. The red, black, and white was kind of funky.. lol.