Does this help?
32 3-pin Red/Green common cathode LEDs.
8 groups of 4, each group has 8 anodes, 1 cathode.
MAX7219 multiplexes by driving the anodes, turning on 1 cathode.
Multiplex rate is 800 Hz, to your eye can look like anywhere from 1 to all 64 LEDs are on together.
It has 8 registers, one for each group.
Bits 0-3 will be one color, bits 4-7 will be the other color. 0b11000011 will turn on two red and two green for example. 0b11001100 will turn on two amber.
I use SPI to drive the MAX7219 when I use it.
digitalWrite (ssPin, LOW);
SPI.transfer(registerNumber); // 1 to 8
SPI.transfer(red_green_color_info); // as described above
digitalWrite (ssPin, HIGH);
Need 5 blocks like above in setup() to set scan limit register (to tell it 8 digits), intensity (brightness, 15 levels) register, normal mode (vs shutdown), no-decode mode (vs decoding to display 0-9 and HELP with seven segment displays), and display test (can be used to turn on all 64 LEDs at once).
