I had a Colt M1991A1 slide engraved with some scroll work and while it looks good, I’m concerned about potential for rust. The company did not put a new finish on it, and honestly I’m just confused.

I’m not sure what the difference between parkerized and blued is in regards to rust. They’re also saying that the material “under the blueing is stainless steel” which doesn’t click with me at all.

Photo attached. Do I need to get this cerakoted in order for this to not turn into a rust bucket? Or are they right and it’s stainless underneath and there shouldn’t be a worry.

Definitely a rust risk.  Thats bare metal

Get some cold blue and see if it will take it. If not, then it is most likely stainless and you will be fine, if it takes the cold blue it will absolutely rust unless you are in the habit of oiling at least weekly.