Well Pete,(posted 8424 days ago)
There are now white LED's that are blue emitting chips with a phosphor coating. This gives a blueish white light. Check out www.ledlite.com Regarding the older 3 element pseudo white LED's, the individual red, green and blue emitters wouldn't have to perfectly "line up" with the color film layers. As long as each element affected its corresponding film layer the brightness of each element could be adjusted to maintain color balance. Also, since the level of illumination is so low balance shouldn't be critical. The big problem with 3 element LED's is a lack of spatial color uniformity.