People can have opinions, you know.

Excuse me? Season 2 kicks Season 1's butt in every possible way!
Intelligence and purity.

I think it's because all the episodes after season 1 were done by a different animation studio. Yeah, it's bad but it does make for fun screencapping at times.

Even as a kid, I noticed the animation style changed with the 2nd season, same with Rescue Rangers. I preferred the original animation. I think they changed the animation studio and the style changed with it,not for the best.

You are not the only one, I too realized that but not on this; but on the Darkwing Duck cartoon. I have a theory but not sure if it is the true thing.
Well Darkwing Duck was a cartoon parody of dark superheroes, so they did the animation with darker colors. They noticed that despite not making the series in bright colors, it was a success and as from there they decided to make the rest of their series with darker tones and less detail to reduce budget but still make a good series. In Bonkers I do notice that day scenes use too much orange and the Aladdin series did not age well.
Though I might be wrong as like you said, you notice this on DuckTales (the Eclipse episode comes to mind, which also had a somewhat dark tone in story as Scrooge was about to be executed, and his nephews were too about to in the bottle cap episode); but maybe it comes from TaleSpin too as some colors looked too "realistic."