well i might be wrong, but here in Texas, ive seen 5%, 10, 15, nitro% in red and green, and the color for the synthetic is always green, and red/pink is always castor based(not always pure castor). but i might be wrong but i dont research that much i just go by what the pattern seems to be. and i usally see GREEN in 15 % by morgan fuels cool power which is all synthetic, and Morgan fuels omega fuel is pink is a blend,and is avilble in 5- 15%
so i guess nobody really knows then