Think about it. In Sonic Generations, Sonic's friends are turned into statues, and their souls are forced to float through some pure white, endless void./tvtropes help
Yes, the ability of Sonic Team to treat dark and serious stories in a carefree, childish manner is astonishing...
If you think about it, Color's story with Eggman enslaving the wisps and destroying the planets was dark, too....
BTW how would you like a GTA San Andreas Sonic Team remake, with Shadow as CJ? XD
Even though Colors and Generations are lighter and more colorful compared to some of the other games in the series, they're actually quite dark if you look into them. Also, I don't blame Tails when he said that he was going to have nightmares from having his soul floating in that endless void. If I were in his shoes, I would too. Even the mere thought of it creeps me out.
BTW, I've been thinking: Eggman's plan in Generations was to undo all of his previous failures so that he would always be the winner, but I can't help but feel that if he did succeed in this plan, he would've went on to wiping Sonic and friends out of existence next.
That's how I see it.