When you find yourself trying to remember a show (or any works) that's on the tip of your tongue but just out of reach, come here - the collective brain of the TVTropes community can probably help. Post all the details you can remember (examples help). If you're looking for a trope, head over to Trope Finder. Have general questions about tropes? Visit Ask The Tropers!
I suspect this is one of the many adaptations of The Canterville Ghost. The bit about the irremovable blood stain associated with the murder of the old lord's wife fits, and her name was Lady Eleanor, which is close enough, and the bit about the blood stain changing colour is what really pegs it (the ghost gets short of blood when they keep removing the irremovable blood stain, and resorts to faking it with paint).
Can't help you with specifically which adaptation, though.
This is almost undeniably it, the whole bloodstain thing is too close to be coincidental. On one hand, I think I've narrowed it down to two animated adaptations, either a 1988 30-minute film or a 1990 50-minute film, however I can't find footage from either to confirm it. On the other, I somehow think that the one I watched must have been a darker/more liberal adaptation of the story, as it seems Wilde's story is more focused on satire. Also, the original makes no mention of Lady Eleanor breaking her neck at the bottom of the stairs or them finding her skeleton in the wall. If anyone else has any ideas about which adaptation I might have seen, that would be fantastic. Nevertheless, thank you for at least giving me an idea of just what the hell it was that I saw.

Okay, this one is really hazy and far back in my memory, but I know for a fact that I saw it. It was either an animated film or an episode of a TV series (though the former seems more likely to me) that aired in the mid-to-late 90s. All I remember is that there was a noble family with a palace that had an irremovable blood spot left on the floor from the murder of the old Lord's wife or something like that. I SPECIFICALLY remember that she fell down the stairs and broke her neck (and it was explicitly stated so in the narration), and I believe she was named Lady Elgin (although that might be something else mixed in there). I can't remember the plot, but I think it involved a group of mystery investigators trying to solve a case. I also remember that the blood spot changed colours after each night which made the investigators think it was a fake. One final detail I remember is that they eventually found the Lady's decayed skeletal body hidden in the wall, with her blonde hair still attached to the skull, which really freaked me out when I saw it as a kid. I know this sounds really weird, but I know for sure that I saw it. Any Ideas at all?