Don't want to take this too far off the 'etching' topic, but both laser and inkjet decal sheets come in white* as well as clear, so white printing can
be done, using an 'inverted' image (lettering as background, body colour as actual printing). But it is the quality of the white backing which many find inadequate (me amongst them). So you either fork out £2200 for something like this
, or find a friend who already has one (but beware, the white toner itself is >£300 per refill)!
*Example of the inkjet version here
, but there are many others.