[ams6110]

You can't change blue light to another color with a filter. The amber light has to be in the spectrum emitted by the lights to begin with. The filter just isolates it.

[maxerickson]

A lot of "white" LEDs have a layer that absorbs some blue light and reemits it at a longer wavelength, with the mix looking white:

http://www.photonstartechnology.com/learn/how_leds_produce_w...

It's not a filter of course.

[ghusbands]

That's overly simplistic - you can use phosphors (and similar chemicals) to change the color of the light. The phosphors absorb light and emit light of different colors. Many daylight bulbs do this.