You can already do this natively: use PNG as mask to the colored rectangle (the PNG needs to be transparent).

For sure, that method works too - just think it’s a little more effort than it needs to be in my opinion 🙂

This method is a bit buggy in previewing, especially when changing the state of an icon, like while hovering. The full rectangle appears first before the mask is rendered.

Rasterize the icon with the changed color before viewing the prototype. But I don’t think using raster icons is a good idea in the first place.