I decided to experiment a little with retroillumination.
My idea was to have a yellow backlight with orange modifiers.
BTW the yellow led I get were more amber than yellow, and were also not to good on beam shape.
So the end result was not too good

So I decided for the plan B, which involves the warm white LEDs.
Again I intended to use warm white for alphabets and cold white for modifiers, unluckily the cold white I got had a slightly different VF so to mix them with warm was impossible w/o cutting and pasting PCB lines (and I'm too lazy to do it).
At the end blue and golden leds were used and the final result is really nice IMHO.
The images are crappy photos but you should get the idea.


I used the color scheme present on model m, but maybe I'll do some further variations.
Warm leds i got are very cheap (less than 10 euro for 100) but very good, they are even, with a good beam shape, and they can be mixed with blue, green and acqua leds w/o the need of separate lines and resistors.