custome sequential tail light.

I would start with red. When it comes to project like this sometimes some trial and error is required for best results.Kevin Pierson

Agreed. Red is cheaper. And the red lenses merely filter out all the non-red colors in the expensive white LEDs. The problem is that changing the color later may change the number of LEDs you can have in a single series string - ie, 3 whites (~10V) or 5 reds, and hence your PCB layout if you want optimum efficiency (les series resistors). (Otherwise assume 3 LEDs & 1 resistor per string.) But that's what the testing is for before the complexity of designing an the cost of a PCB. Though a blank or "donut plated" holed matrix board may suit your LED & reflector spacing..)

To oldspark: I will most likely go red, as that is the color of the lens. And there will be something like 130 LED's per light and two lights

I wonder if somehow it would be possible to use the logic part of an old chaser light bar. Think KIT from knight rider. At least for the sequential part. Treat the entire assembly as one unit for the parking light and brake. That should be fairly easy. Lots of relays and diodes I am sure.

No relays. And none needed, nor desirable. Many of those KITs used 4017s.