Thanks for trying. I should say that it is solid wood and this is a floating (is that the right term?) panel. There is a crack running through this piece but it's still stuck together. Maybe it's 2 pieces glued. Anyway, no plywood or veneer.

Any idea what wood it is? :)

I'm guessing that it is spalted pecan wood...spalted : the darker areas.

Interesting! That sort of fits. It must have been less obvious when the things was built--doesn't really go with the "style" of the armoire. Or it happened after assembly. The more I look at it, the more I think that this one panel was made from 2 pieces, and both show the discoloration.

It's not discolored or stained; it's the natural appearance of heartwood and sapwood of that species of wood (whatever it is) when they wood is varnished or given a light stain. It may have darkened a bit over time, but it probably had this much contrast on Day One, and is more noticeable because the panel is not stained a dark tone. You can see that the dark wood is wider at the top edge right where it transitions across the raised panel; that happens because the panel is solid wood and the heartwood is wider as you go deeper into that piece of wood. If you didn't have the raised panel, the width of the darker wood wouldn't change at the line that demarcates the raised panel. I have a 20-year old house with maple doors that just have a lacquer finish, and I have had the same contrast on them as you since I moved in because of the heartwood/sapwood contrast:

Embrace the look of your armoire as it's natural and there is nothing to "fix." ;-)

I won't be fixing it!

It's been like this as long as I've had it (longer than I care to admit) but it's been recently moved so the spots aren't facing a wall. And thus my curiosity was renewed.

The inside isn't stained or varnished (shellacked?). Here's the spot on the inside:

As you can guess, this armoire is full of stuff. And I can't reach the top shelf well enough to get a better photo.

Your last photo is more evidence of solid wood construction, and high quality wood as it hasn't cupped or warped all these years.