I've never seen a backlit version, and I'm positive they don't exist
well not the whole key is clear. i have a CM Storm Mech and the CM storm keys are black with a "clear" letter
That's because those are not doubleshot. The whole cap is made from a semi-clear material and has a black coating to block the light everywhere except where the legend is.
The WASD keycaps are single colour ABS with pad printed legends if I am not mistaken, so they're not backlit.
SP can do ABS / polycarbonate doubleshots, but they have support grids in the mold and can look a bit odd:
If they use semi-opaque white PC material with black ABS base material it could look quite nice. Not sure what they'd charge for just a few, though. They should already have the Lambda mold (since they made the black and orange SA profile caps), but I'm not sure if it can be used with DCS profile base.
Also be aware that SP's DCS profile is not the same as the OEM profile keycaps that come with your keyboard (and neither is the SA profile orange and black Lambda cap), so it will be a different height to the other caps on that row of your board.