ATtiny13 microcontroller has 6 available I/O’s, so there is no way to drive seven RGB LEDs directly. Well, CharliePlexing will not work as well as there is still a lack of pins. But if we look deeper in problem we can find that dice LEDs can be grouped in four groups that makes possible to control total 12 LEDs.
There is also one button used to fire random number generator that generates number from 1 to 6. Using RGB LEDs for such project is quite overkill but final effect is great.