It has to do with what color sun light is present during different seasons. Based on the tilt of the earth closer to blue is around during spring outside the tropics; closer to red during fall again outside the tropics.
As I understand it 6500k, blue, is better for growth, closer to 3000, red, better for flowering. Peppers grow and flower at the same time so a mix is great. If you have the patience using all 6500 until plant are ready to flower then a mix is ideal... as I understand things.
- Mega