two color led 'blink' sketch- low power on one color

Projects Programming
6 
void setup() {
  // initialize digital pin LED_BUILTIN as an output.
  pinMode(LED_BUILTIN, OUTPUT);
}

You need a pinMode for the 2nd pin you want to use.
setup() only runs once, after a reset; if you only use pinMode once, only 1 pin gets set up as an output.