The question is: have all these 24 rows been multiplexed one-by-one or is there a couple of shift registers loaded in parallel? By other words, is refresh duty cycle 1:24?
The multiples is as follows:
Loop:
strobe, unblank 4ms/n
while that upload
strobe, unblank 2ms/n
while that upload
strobe, unblank 1ms/n
while that upload
strobe, unblank 0.5ms/n
while that upload

This allow different intensity of the color LEDs to give an intensity in 16 steps of the R,G and B

What is about that such duty cycle value decreases bright alot? By making all color mixes a total of 15 the brightness is alway equivalent to 1 LED on constantly (if the required color is red, red is on in all timeslots = 7.5ms - if orange, green and read are both on for 4ms ~ same intensity as red).

For proprietary reasons, I can not explain further

Erik