I wanted to know if their are any slow growing colorful plants I could add to a new 55 gallon tank. These plants would have to be able to grow in gravel. I dont see any option to add soil/sand, unless someone has some colorful ideas...
What you can grow, depends more on lighting. What do you mean by colorful? In general, most plant that can produce red and/pink colors require higher light.
Give us some info. on your tank.