You can find replacement notebook chargers on ebay that will meet voltage/amp needs. I’m looking at a lenovo 18V/65W
Most RGB leds can support either .35A or .7A which picobuck can drive. You can drive multiple RGBs as long as power supply voltage - 2V > total voltage drop. You should be able to achieve your colors with PWM right?
this will be a a vehicle - hence the 12 VDC supply. So your suggestion is to run one per colour on the LED R +G+ B - then adjust brightness of each vice a PWM controller to the PicoBuck?
I am guessing the pico buck can support LED in parallel ?