Petey,
I briefly touch on that in the first paragraph of the box for a panel  but generally I'll mix up some strong dye concentration (TransTint) in a small plastic bowl with alcohol and put the pre-cut parts into the bowl. The bowl (and a few others with different colors) are put into a two-gallon vacuum pot and  held at a vacuum for a few hours. I'll then release the suck and let it sit for a few more, then repeat. I'd like to keep the veneer in sheet form but the pot is too small for that.
Some woods can get completely saturated from this, but others like maple need more. So then it is into my pressure pot at 75 PSI over night (as high as the pots gasket lid will allow).

This usually gets the 99% mark.

I'd like to try Shipwrights method of boiling in RIT cloth dye sometime, certainly a lot less expensive than the TransTint!