Found this on MTBR forum:
there is a reason carbon black is added to rubber for tires, it has the highest
molecular surface area for reinforcement of the polymer chains.
it improves its tensile strength and wear resistance
skinwalls are weaker, since there is far less reinforcement and wear resistance going on in the non-black rubber
in fact any other color than black is weaker or the tire behaves worse in some way.
run them if you want, expect them to degrade sooner
Practically all rubber products where tensile and abrasion wear properties are crucial use carbon black, so they are black in color. Where physical properties are important but colors other than black are desired, such as white tennis shoes, precipitated or fumed silica has been used as a substitute for carbon black in reinforcing ability.
Traditionally silica fillers had worse abrasion wear properties, but the technology has gradually improved to a point where they can match carbon black abrasion performance.
advanced fillers are not in your gumwalls, your gumwalls are closer to raw vulcanized rubber.
I won't be buying gumwalls again for sure. Merlin in the UK has a clearance sale on Jumbo Jims - looks like just over $100 for a pair including shipping to USA 