Alright, since no one wants to say anything bad about this, I'll step up.
I'm going to apologize in advance for being really nitpicky, since... well, there's hardly anything to talk about. My first suggestion is to not start a thread when you only have GFZ1 with a different palette to show off. If you're trying to build up hype by hinting you have more to show off, it doesn't work (on me, at least) because there's pretty much nothing here to get hyped about. If I showed a picture of this to someone who hasn't seen this thread, would they think this was a Sonic 1 remake, or just a palette mod?
Next, the title screen. It looks very... eh. The SRB2 Sonic and the S1 ring both clash heavily and it makes Sonic look like a giant and/or the ring look tiny. I'll admit, the beige version for the intermission is a neat touch, even if the idea's taken from S1's level select.
Finally, the palette. The whole reason I wanted to make this post was so that I could warn you: you're making a lot of mistakes I made in older versions of Color +. First of all, the new blue clearly looks out of place. Its hue is also off, making it look more purple than S1's desaturated blue. The green and gold look like they had their saturation turned up full blast, and I'd imagine it'd be headache-inducing looking at it for a prolonged amount of time. I see where you're coming from, you're trying to make it look more colorful to accommodate the graphics, but I think SRB2's colors are already vibrant enough to do this. For example, GHZ's walls could likely be imported with the current orange colors; you don't need to make gold look worse. And lastly, the yellow looks really dull and gross on the HUD. In S1, it's only a tiny bit off from plain yellow, so I have zero idea why'd you want to make it even murkier than 2.1's yellow already is. EDIT: I also only just noticed the S3K bubble shield because of the brightness of the palette. That's probably not a good thing.
While I am curious about where you could take this, there's nothing to really go off of to make me excited for this, and what there is not very impressive or I feel aren't very good changes. However, it's really hard to tell what your trying to make here. It's mostly just graphical changes, and that doesn't really tell us a lot about a level pack.