I'm surprised anyone does. Although I didn't realize there were games that ran on GBC but didn't run on GB. But essentially it was what it said it was, a Game Boy with color. I guess the fact that it had a bunch of exclusive games makes it an oddity more so than other Nintendo revisions that got like 5 exclusive games, but neither Nintendo nor consumers ever considered it a separate system. It would be like if the Switch "Pro" that was being rumored, in which it is just a more powerful revision of the same system, and people were hoping it'd get a library of Pro-exclusive third party ports from the consoles. That wouldn't make a Switch Pro a different generation or different system than the Switch, just a revision powerful enough to warrant higher spec'd games that can't run on other models of the system. That's I suppose precisely what the GBC was.

As a teenager at the time, who had a GB, I considered it a color version of Game Boy. Never even knew there were any exclusive games. I knew there were games made specifically to take advantage of it's color abilities, and that was it. I don't think anyone at the time was thinking that they were getting a new system when they upgraded from GB to GBC. I get how the exclusive games that it apparently had can make some sort of argument about it, but it is very clear that Nintendo has never viewed it as anything other than an upgraded revision of GB, and I've never seen at the time or since that the market considered anything different.

I've posed this question online before. It's kind of both.

Arguments for it being a successor

• Identified as such in an Iwata Asks Interview
• Released 9 years after the Game Boy
• Over 2/3 of the library is incompatible with the Game Boy. I know people can point to New 3DS games that don't work on normal models, but there were far less by numbers and percentage. Same with trying to use the DSi argument. A lot were digital too, and the Game Boy Color was before digital distribution. Nintendo made a conscious choice to have a lot of the games not run on Game Boy. 

Arguments for it being a mid-gen upgrade

• Very similar form factor, and identical controls.
• Hardware sales lumped together with the Game Boy.

I can kind of understand why people think it's a refresh, but to me it's closer to a successor than anything like the DSi, New 3DS, PS4 Pro, etc.

As an owner of the original Gameboy, a clear "Play it Loud" Gameboy, and a Gameboy pocket, when the GBC came out, I thought of it as "Just another Gameboy". I didn't buy it. Despite having a few exclusives, it just felt like a minor update.

I jumped on the GBA, though. That felt like a true successor.

When I think of Nintendo console history and I list Nintendo consoles, I never even think of the Gameboy Color. It's like it never existed. ?

Hardware revision. Having games that can only be played in specific models isn't enough to distinguish two gens.

For eg: Switch Lite cannot play Nintendo Switch Sports nor Ring Fit nor Super Mario Party, doesn't mean it's not the same gen as the Switch.

When you put a GBC cartridge in a regular GB (or at least the revisions which doesn't include the stick that comes out when you boot the game, such as the Light and the Pocket), it says "no no no, please play this game on a Game Boy Color", it's very specific

The jump is not nearly enough to consider it another platform.

You mean jump in all aspects (specs, form factor, controls, etc.), right? Because if you're only referring to a jump in specs not being enough, then the Wii or Switch wouldn't be other platforms than their predecessors either.