On the internet there are lot of instructions about connecting RGB LEDs and Arduino but nothing about controlling brightness except connecting potentiometer to every LEDs input but what when you don't have enough potentiometers? Then this instructables will help you.
Step 1: Parts List
You will need:
RGB LED module (if you don't have RGB LED module but only RGB LED you will need to connect 330Ω resistors to led)
Step 2: How to Connect
Step 3: Code
With potentiometer you can adjust brightness of actual color and with button you change color.
Sorry for my bad english.