I'll be shocked if they retain the colors/bezels of the 24" for the 30"/32". I don't see it happening.I don't think that the new big iMac will be known as the iMac Pro, given that the brand got killed just a few weeks ago. However, if you think that the iMac Pro's discontinuation was related to issues with Intel Xeons (shortages and inadequate enough margins and sales volume to justify restocking), then there's certainly a good reason to believe they will revive the iMac Pro branding. So I see an argument to both effects.
Personally, I don't think that it matters if they call it a 30-inch iMac or a 30-inch iMac Pro—what does matter, however, is the starting price. I don't think that they can ask for a sum at all comparable to the Intel iMac Pro's $4999 starting price if they will put an M1X in it. Maybe models that come with those rumored custom Apple GPUs could be optioned up to such a price, but I feel like the new 30-inch iMac has to start at $1999. Apple silicon increases Apple's margin, so I see no reason for a marked price increase.
As for the colors, I am personally hoping that they let the 30-inch iMac have the same bold and vibrant selection as the 24-inch. If they choose to brand it as an iMac Pro, however, the color selection will be analogous to what we see in the "pro" iPhone line, that is: white, black, gold, and a more reserved wild card such as pacific blue or midnight green. Both scenarios would be fine by me. But, either way, I'd expect the larger iMac to keep the same design language as its sibling, if a bit thicker to accommodate things like an SD card slot and USB-A ports.
Also a shame Apple doesn't make a nice split keyboard (two halves). I use one by Kinesis and it is ugly as sin but has completely changed my life.