Oh crap. I’ve used the white on my boat for years, didn’t realize there was a difference between it and grey. Thanks for that.No. Well, yes, but no. Marine Tex white has a much lower compressive strength than grey, and IMO, isn't suitable for bedding. It's intended to be flexible after curing for fiberglass repair applications. Grey is for machine repair and is much harder, but also more brittle.
That said, it will probably work fine for a low recoil job like a 30-06. Yes, it can be tinted with resin pigment. I do that often for fiberglass repairs that need to reasonably color match gel coat.
Jeremy