|RGB LED Matrix Schematic|
If the LEDs seem to flicker you are not updating the RGB matrix at a fast enough rate. To solve this reduce the amount of time between the calls to UpdateRGBMatrix().
bit_twiddle.h -- Helper functions for bit manipulation in integers.
RBG LED Matrix Datasheet
http://marc.merlins.org/perso/blog/cat/arduino/post_2015-01-06_Driver-for-direct-driving-single-to-3-color-LED-Matrices-with-software-PWM.html (Great site with lots of details and optimizations)