I think you're in the wrong forum - (don't see any previous messages
from you here in Typography).
This isn't a typography question - it has to do with print preparation
in whatever application you're using - Photoshop, InDesign, or
Illustrator. You have a better chance of getting a good answer in the
appropriate application forum.
You mean like this?
It's easy. In photoshop (and yes, this is more of a photoshop question rather than a type question) If you have the text on a layer above the background (green) temporarily change the background to black. So you just have white text.. Select all and copy merged. Undo the black from the background so it's how it was.
Above the text create a new layer. Fill it full of green. Create a new layer mask, paste in the black and white image we just copied as the layer mask. That'll give you the "green" area in white. You'll need to clean up the masking by turning the white text to black. But that's pretty much it. Hope this helps