I just saw his light a bit ago. Looks plenty red to me when it lights up.

A white LED is actually a BLUE LED. They then put a thick layer of phosphor over the LED. That reduces the blue, and converts some of it to red and green. Thus it looks somewhat white. So when you put that behind a red lens, and you of course get the red light, you just threw away most of the blue and green light. Roughly two thirds of the light is thrown away when you use white behind a red lens.
But if you get a RED LED and put behind a red lens, most of the light is used. Usually.
(I have heard that some odd colored lenses and LEDS don't match up very well and they even block a lot of the red from a red LED.)