It all depends, really. The new light might have a different mounting plate/bracket, etc. which can be a pain, especially when working over your head. If you're handy with that sort of stuff though, it should be doable apart from, as you say, needing to see the colors of the wires.

Even if they don't want to change it, could someone else in the house describe/label the wires for you? You could test with a voltmeter with the power on (provided it gave audible feedback), but that's unnecessarily dangerous if there are other people around who can just go "Yeah, that one's white."

I would imagine there's no scenario in which you can properly connect these wires to the new light without vision unless you're at some point touching bare wires, so definitely do make sure that the breaker is off.

As long as you can have a sighted person tell you the color of the wires, this wouldn’t be a problem. Wiring is, imo, the easy part. Getting the wires to lay correctly in the box so you can mount the fixture is often the hardest part. Just make double sure the right breaker is OFF.

It depends on how comfortable you are doing that sort of thing. I've done wiring all of my life, wired my own house. Doesn't sound to me like you'd have any trouble.

Burning the house down with the ellectrical accident could be expensive..

I’m sighted and worked with my dad (who is an electrician) as a summer job for a few years, and even then I wouldn’t do my own wiring without my dad there to verify I’d done it right. Having the breakers off will protect you from being shocked when doing the work, but if the wiring is done incorrectly it’s an electrical fire risk. Really wouldn’t recommend it to anyone untrained, regardless of their level of vision!