The blue LED was the last LED light color needed to produce white light in combination with green and red LEDs, IIRC.
It turns out to work better to use a blue(ish)* LED energizing a white(ish) phosphor.
In fact, if you look at the spectrum of a white LED there will be a broad output in the warmer colors and then a spike of blue.
*Older “white” LED’s in particular often still have a purplish cast to them. The phosphors have come a long way too.