If we take everything we know about bass including the things you have mentioned; that they eat their fry during certain times, that they do not all spawn at the same time, and that they are opportunistic feeders, we can draw some pretty favorable conclusions as they relate to baby bass colored lures.
Because they eat their young, the lure should work pretty efficiently during certain times of the year. But, because bass do not all spawn at the same time, you can see that the window of opportunity in which you can use the color effectively, becomes a lot wider. Even if the fish are well beyond the point of spawning, being the opportunistic feeders that they are, if you present a baby bass colored lure in front of them at any other time of the year and the conditions are right, I see no reason why a fish wouldn't target the lure.
Finally, as others have stated, the lure also probably works simply because it is such a good "natural" color. Think of how many other fish or animals for that matter might have the same broad coloration in the body of water you are fishing in. Some species of sunfish, frogs, insects, perch, etc etc have many of the same colors as do "baby bass" colored lures. Particularly, if the lures are presented "at speed" and you draw a reaction bite, a fish usually isn't going to stop to see how naturally colored the lure looks. Instinct dictates that this fish will likely operate under "Eat first, ask questions later"---especially when the lure is as naturally colored as are baby bass lures.
You can probably tell that I have enjoyed pretty good success throwing "baby bass" colored lures. I do not have much money to spend on lures and the fact that the majority of my lures are this pattern---you can tell how crazy I am about them.
PS.
I caught this fish (my pb) in the very middle of summer. All fish were probably completely spawned out by this point. I had not gotten a freakin' bite all day, 4 hours of fishing to be exact. I was getting ready to call it quits and decided to change up the color and throw a baby bass version to my cotton cordell lipless crankbait (love these things). I landed her on the first cast of this bait in this color....