I'm using the TLC5940 PWM LED driver. No multiplexing... the rows are identical outputs. This is done with some nested loops and some trig (sine wave conversion).
I'm sure I could have a potentiometer control 1 or more of the variables used in the loops above to either fade the matrix to a specific color or just take the scrolling part out of it and have the potentiometer just send static values to be used for the color calculation.