Fishing is all a game of probabilities (at least, that's how I view it). On any given cast, with any given bait, you either will or won't get bit. Over the course of a day, if you can stack a few more probabilities in your favor (increase specific probability rates or percentages), you should end up with a more productive day. There are a lot of variables at play, all with their own probability. Color tends to rate fairly low on my list of probabilities. What do I mean by that?
In another thread I mentioned that one of the 2 primary factors in why I own/throw whatever colors I have in my box for any given bait is largely based around what is pretty much "proven" as a standard color option. So, a black and blue jig is almost a universal thing. A green pumpkin soft plastic is too, as are things like shad or crawfish colored crankbaits, a white and chartreuse spinnerbait, or a black or white buzzbait. I'm sure you can name a few others. Day in and day out, those colors get bit most everywhere in the country. As such, I tend to have one of those standard color patterns tied on when I'm fishing, and I rarely change during the course of a day.
But here's a logical way to think about lure color based on probabilities. If you're not getting bit, it's probably not because of color, but it also might not hurt your chances if you changed. Things can't get worse, right, so do as you like - I likely wouldn't change myself. I'd rather change locations, baits, depth, speed, etc. before changing color to try and increase my probabilities.
On the other hand, if you are getting at least a few bites, changing color could go one of several ways - your bite rate might not change at all (neutral), or it could get better, but it also could get worse, and you actually might stop getting bit. In this case, which is likely the most common scenario for most while out fishing (getting a few bites now and then), I don't gamble and change my probabilities in that regard because there is a worse outcome if I'm wrong.
Finally, if I'm with someone throwing a similar bait (different color) and they're getting bit and I'm not, then it doesn't hurt to change to whatever color they are using because your probabilities will likely either stay the same or go up - very little downside to changing color in that case.
So that's my take on the matter. To stick with the OPs question; why do dark colored plastics catch fish in clear water? I say - Contrast. About everything swimming in the water (or tossed by anglers) throws shade/has a dark underside no matter what its actual color. Bass eyes are built to best see forward and upward. As such, black is a universal base color in my world - YMMV
-T9