Any of the micartas, G-3 or G-10 phenolics are "plenty" strong enough. The reason for the Randall shop to only offer green or black micarta is that the material has to be sent out to an outside source (sub-contractor) to be sized and, in particularly, "slotted".
You can supply your maroon micarta to the shop, but it has to be already cut and slotted to their exact specs. I have several pieces at the shop at this writing to be done. Jim Behring (Treeman Knives) has some sort of brown canvas and green tenite micartas for sale on his website. They are already prepped for Randalls...ready to go! Hope this helps.
Best, Capt. Chris