Large pickguard would place it somewhere from '65-'69. With the reflector knobs and nylon-saddle bridge, narrows it down to around '65-'67. Shipping totals are pretty easy to find on the web, but they're not broken down by color. Regardless, the custom color Gibsons of that period are much rarer than the standard finishes, and accordingly command a pretty good premium.
BTW, the official model designation is the SG Standard (w/Lyre Vibrola). Lots of folks are turned off by the skinny neck on the late-'60s SG's (1-5/8" width at the nut), so that keeps the prices down a bit. Still not a cheap guitar at all.