No ash gray flooring. No. Please. It was a fad , and it has sailed away.

Put an edge to edge carpet RUNNER on the descending stair, and whatever wood you select in the basement ( not gray ) and that need not match the main floor.

Know that there are codes for stairs, and the slightest variation matters greatly, especially riser and landing points.

We have a professional coming in to do the work I've just started looking at colour samples. I take it you don't like grey?? lol. :-) Ultimately I wanted to avoid old fashioned "dark" wood but not totally sold on grey...maybe just something light.

Basement and main floor do not have to match.

Stairs do not have to match floors either, if there is a decent contrast - as opposed to "tried to match, but missed".

I've had dark and light hardwood floors, and the darker wood showed every speck of dust. Our current oak floors with no stain don't show dust at all.

for the basement floor, I would find the lightest flooring you can find, steps don't need to match anything.

You just want to avoid the gray tinted LVP. It was very popular up until about four years ago. Now it's about as popular as poison ivy. Even house flippers have stopped using it. That's when you know a trend is dead as it can be.

There's nothing wrong with liking gray. Have a gray sofa, a rug with some gray, but more natural colored floors are now popular (on the light side), and aside from what is on trend or not, it just makes more sense to use a more natural looking flooring. I have LVP in my basement that is on the dark side (medium to dark) and it doesn't show dirt. I love it. When I had it installed five years ago I had to look hard for something that wasn't gray at all and I'm glad I did. IMO a medium tone is pretty immune to trends. Let everyone else flip flop back and forth between light and dark. If you get something that is close to the upstairs in shade, but the stairs are carpeted or have a runner, no one will notice they're different. I have carpeted stairs to ease the transition.