I would let this one go. In the pictures, at least, the difference is subtle and doesn't bother me at all. It looks like the flooring was factory-finished, the stairs finished on site. If the processes and materials are not identical, so you shouldn't expect their appearance to be identical. Your contractor might manage to satisfy part of your preference, i.e. make the stairway less reddish, but cause some other problem in the process such as making the stairs noticeably darker. The risks and costs of futzing with this are real, and the potential benefits seem small. Unless the photos are misleading, I'd focus my energies elsewhere.

Thanks for the advice everyone and Susan Davis for the photo inspirations! benjesbride I know... people seem to have a special kind of dislike for corner fireplaces :) I don't love it but I'm stuck with it. I'd remove it but I think in my area/neighborhood a fireplace would be expected, and it would be very tough to move it. So I have to work with it. I think if we were to get a big tv we'd need to build a space for it in our basement, maybe someday. I don't really want a gigantic one in this space :) Also perhaps it's hard to see from the photos but I don't think the tv would fit on the stairwell wall... just not enough space. We do plan to add shades to the windows, perhaps the wood/bamboo type to add more warmth. In general I feel this room is a bit awkward... but trying to make it work :)

Laura,,Poplar is more of a paintable wood rather than stains. to get a true ebony stain color you could try a black aniline dye first, and then go over it w/ebony gel stain. I did it with my oak and got it very black. otherwise, just use a good enamel paint for wood in the same black color as the wall. and no, stained wood doesn't necessarily mean it will hold up better. if the handrail is properly prepped, paint should hold up fine. But try the ebony stain first, if you like. I also think Polyshades has a black stain/poly all in one.(I would still do the aniline dye first because it will give you a black base. poplar has a tendency to turn a little green. the black stain may not be enough to completely cover it. see table below)

Maybe, definitely yes, absolutely not, it all depends. How about pictures of the area in question? What other colors are involved, walls, etc.? Impossible to really offer much without context.