[djahng]

The LEDs are typically blue with a phosphor that is energized by the LED light. It's the phosphor layer that starts to glow and produce the white light.

If you "paint" a surface a particular color to alter the light transmitted through it, you're effectively creating a filter. If you want something to appear more yellow, you need to increase the amount of yellow wavelengths transmitted through the filter by reducing the other wavelengths. But if you have a single color LED, such as blue, there are no other wavelengths present (at least not in any significant amount). So if you put a yellow filter over a blue LED, you see nothing...