This may be worthy of reading:

http://pinside.com/pinball/forum/topic/expsoure-concerns-over-blue-purple-leds

I mention is because, while using blue LEDs on a playfield might not be so bad (the light is indirect generally), using blue LEDs firing directly at you? Some research suggests that can actually be bad for your eyes. Normal blue light tends to have a much larger white component than a standard blue LED. I have the same problem with the piecing blue others have here and I suspect that's one reason.

White LEDs still tend to have more blue light than, say, a normal incandescent white bulb, but are much better than pure blue LEDs. I'm just guessing, but I suspect using white LEDs + a blue filter may be allowing for a lot more of the color spectrum than a typical blue LED has which might be more pleasing to the eye? Just guessing.

Blue LEDs look really cool, but I personally don't want them firing at my face while I'm trying to concentrate on pinball. Of course, everyone is different, YMMV, Carpe Diem, etc.