My Excel experience itself is relatively limited, and last night was my first foray into conditional formatting.
This is one of those times where there really is no substitute for sight when it comes to figuring out exactly what's going on with the screen reader itself, which is behaving as it should, but with a dialog setup that is quite atypical and where what you hear isn't always exactly indicative of what's going on. The fact that "No Color" is a button with a value of its own, and the first one, can lead to the utterly incorrect conclusion if one lands on it again that you've somehow undone a color you set earlier, but you haven't unless you press it. The screen reader also never lands on the large graphic at the bottom of that dialog that is showing the color sample in a broad swath that you selected above, which does make sense since you can't interact with it, it's meant as an obvious visual cue for the sighted, but even they can't interact with it, it's just there.
I do all these sorts of checks "as needed" because I've learned over time that non-intuitive dialogs can be confusing enough when you can see them, but when all you can do is hear them, and you aren't quite certain of how they are traversed, it makes it even worse. I was actually surprised at the whole need to right arrow through the "short list" of colors at the top before landing in the grid where all the directional arrows work. This is not something I'd expect anyone, including myself, would know unless they'd already had experience with it. It's quite peculiar.
Brian - Windows 10 Home, 64-Bit, Version 1803, Build 17134
A little kindness from person to person is better than a vast love for all humankind.
~ Richard Dehmel