Color change does affect value but really, no one is as fussy as are vintage Corvette owners about every little thing (just kidding, but you know what I mean) . So my opinion as an appraiser and not an SL "expert"-- is that "it depends" on a) what the color change was---from what to what, and b) how well everything was done.
Another complication is the "grade" or quality of the car. Obviously, a "driver" SL with lots of other needs isn't going to suffer as much with a color change, because it probably needs a complete restoration anyway.
An example--I recently saw a black car that used to be white. It wasn't a good job, and it was also a regrettable switch of colors--white would have been much preferred. So every chip, every missed spot on the repaint shows up immediately. On top of all its other problems, that particular SL would be lucky to pull $40K.
The statement made here that "values are all over the place" is really true, which makes it difficult for the newbie to know what to pay. It really depends on what level of originality, correctness and condition you want.
I saw an absolutely beautifully restored Pagoda sell for $150,000 not too long ago--it was perfect down to the decals on the electrical relays. Even the grommet that holds the windshield washer bag was NOT aluminum (oh, no!)--it was the correct metal color for that car, that year.
So yeah, there's "restored" and then there's RESTORED. That's the difference you see in values.
It might be a good time for you to buy. Values for Pagodas have definitely slacked off since early 2017. Even the most magnificent ones haven't yet regained the levels they had 2-3 years ago. You'll pay more for a manual transmission though, especially one with AC. When I worked for Mercedes, I bought a new one, 1971, green w/ tan interior, manual transmission and AC. To me, that's the best possible combination of everything for a Pagoda.