Would it had made more sense during Red Sky if the Earth was in Dimension X?
 

Before the Red Sky era, the only time we'd see an actual red sky was in Dimension X. Since the technodrome after Shredder Triumphant was pulled into a Dimension X black hole, I feel like a big cliffhanger after that episode would be that both the Earth and the Technodrome finally got stuck into Dimension X and Shredder was indeed "triumphant" in terms of sucking Earth into Dimension X that failed back in the Big Blowout, but someone like Bebop or Rocksteady screws up the Technodrome's course when it goes through the portal and leaves the Earth in a distant part of Dimension X. A big "to be continued... Earth in Dimension X" could have happened after the Season 7 finale, keeping fan interest for the new season, which WOULD expect fans expecting a darker plot and, most importantly, a red sky. It would make sense then in Get Shredder to see that red sky, which would clearly indicate "Earth is in Dimension X". But I would have ended the series with defeating Dregg/Shredder and rescuing Earth back to its proper dimension, turing the sky normal again and having a proper finale, clearly showing that the Turtles have completed their adventures and peace is finally here to stay.

Nobody ever complained about the red sky in B:TAS.

It doesn't bother me, and I don't believe there had to be an explanation for the red sky/darker tones. BUT, I like your idea too :D. I would have liked for the series to have wrapped up in an all-encompassing finale. That said, Turtles Forever finished everything off nicely(I still wish they had tried for the original voice actors).

No no no no no. I liked everything that they did in the Red Sky era just fine thank you. No need to change anything that they did during those episodes.