http://www.ti.com/lit/ds/symlink/tlc5951.pdfEach TLC device will control a row of LEDs. Eight devices will control 8 rows, that's 1 layer. All the anodes from 1 layer will have current sourced from 1 PNP, or P-channel, device.All the LEDs in a column get their cathodes connected in parallel, to a single TLC pin.Send out TLC data for 1 layer, enable that layer's current source.Repeat the next layer.
Source goes to the RGB LED anodes. LED cathodes go to the TLC pins.What you are doing is selecting which set of LEDs are having current sunk thru them by the TLC.