I assume you know that you will need to put the other two bolts in the carrier and remove the Case thingy that is presently attached to the carrier. The Case goes on a standard 4-bolt carrier, but you remove the other two bolts and install a hanger when mounting it. So presumably, but not definitely, you will be able to use the carrier that's in the wall, but you will have to get to it and do those modifications before installing a Glenwall or other toilet.
You've only got white, linen and bone these days in the Glenwall.
The Gerber Maxwell only comes in white in the wall-hung.
There used to be a third manufacturer, but I can't remember/find it right now. Maybe discontinued.
But those are your choices for a wall-mount, non-tank-in-the-wall setup. You can put the tank outside the wall with a Geberit Monolith, onto which you mount the tank-in-the-wall wall-hung bowl (like a Duravit Vero 221739 wall hung, which is black), but it's expensive to do so. The Vero in black, best price, is gonna be a grand, and the Monolith is gonna be at least $900. For that kind of money, you can get an amazing plumber to repair your Case 3000, which is a great toilet.