Curious, I kept digging. As it turns out, in 2006 and 2007, the predominate base colors were different, as (I guess) new batches of vinyl were ordered and slowly painted over the course of the year.
Anyway, here's what I came up with:
In 2006, clear vinyl was Koiwa-san's base of choice for Maverasu. (Technically, the first clear Maverasu was released in late December, 2005 - a clear green Mav that came in the Cronic Christmas tin can set.)
Koiwa-san created some amazing clear figures in 2006, including regular spray, pinstripe, and (meticulously) stuffed versions.
There have been exceptions, like the Max Toy exclusive painted (and unpainted) clear figures. Also, with the Maverasu Handpaints, it's not possible to tell what the base color is (without disassembling the figure!), since every part, including the bottom of the feet(!!), is painted. Still, the majority of new versions this year have had GID vinyl bases. (I count 5.)
So there you have it. If the pattern holds, maybe we'll see a new base color making it's appearance in late 2007!