"What exactly IS the color of Mahogany if it ages without sealers, etc?"

Gray, like the vast majority of woods.

There a very few solid mahagony doors out there. Most solid wood doors are a less expensive core with a mahogany veneer. You should be aware of this so you don't sand through the veneer, if this is the case.
Be that as it may, your best bet may be to put a clear finish on the door and let the color take care of itself. It will darken soon enough.

Initially it will be kind of a greyed pinky-orange or grey-brown (if you know the colour of unfinished mahogany you'll know what I mean), if the doors were finished when the wood was new. At least, that's the colour of some mahogany baseboards I recently stripped.

And if it really is stain, as opposed to a coating, you may have some residual colour.

KarinL

Yes, they're solid.

"...put a clear finish..." What type?

KarinL, finished with what when new? And really stain as opposed to coating? I stained them (long story and against my better judgement) and coating? What type of coating?

Thanks,
Christine

I've read in several magazines, articles, etc. that the best finish for old wood is varnish. Polyurethane is great for new wood, but varnish is recommended to be better for old. I haven't tried it yet but I also have some doors that need to be re-stained and I'm planning on using varnish.