8x8 RGB LED PWM matrix with TLC5947 which IC to use on the cathode end?
I commend your ambition, but not your choice of projects (at your apparent level of knowledge). What you need to do is apply a PWM which varies depending on the row which is selected.

In principle this is pretty straightforward, but it's not easy. You would make 8 PWM generators, one for each column, and when you select each row you would load the appropriate PWM control value into each generator. Maybe you can go to this website:electronic parts 

As you might guess, this will take considerable hardware. While it's true that some MCUs generate PWM outputs, I can't think of any with 8 such outputs. A compact solution would be to use an FPGA to do the job.