is it possible to get a 26" tyre in any other colour except black?
around size 26x3
no
For a while Michelin made a 26x2.5 tire in red. I think it was called the “Hot”
I’m pretty sure it’s no longer made, but you might find one somewhere.
You can get different colours in the smaller (more popular) sizes like 1.95 or 2.1. It might be hard to find anything larger than that that isn’t “tire colour” as surly says.
If you are desperate for a different colour you can sew a couple skinnier tires together, or spray paint your current tire…