Wordcrafter today tells us the words: isabelline; isabella; isabel – a dingy greyish-yellow color, as of unwashed underwear

Spain's Phillip II, he of Amada fame, had a daughter Isabella. On her 1598 marriage to Austrian Archduke Albert he provided as dowry his posessions in the Netherlands, which were in revolt.

In 1601 the Austrians laid seige to Ostend. It is said that Isabella
vowed not to change her linen till Ostend was taken; this siege … lasted three years; and the supposed colour of the archduchess's linen gave rise to a fashionable colour … whitish-yellow dingy.
Various stories have been put forth to account for the name. That given in D'Israeli Cur. Lit. (Article Anecdotes of Fashion), and also in Littré, is shown by this OED quotation to be chronologically impossible:
" 1600 (July) Inv. Queen's Garderobe in Nichols Progr. Q. Eliz. (1823) III. 505 Item, one rounde gowne of Isabella-colour satten,..set with silver spangles."
Thus poor Isabella has been ill-favoured and ill-judged. Rumours of smelly and offensive coloured knickers have been greatly exaggerated.
But how did this epithet arise?

I just assumed that the story, correct or not, was the impetus for this word. It has happened, I believe, that words have evolved from information that has later been found to be false, though I can't think of one right now.

Uh, haven't we made a logical error here? Contrasting:

• Isaac Disraeli: In 1601 the Austrians laid siege to Ostend. It is said that Isabella vowed not to change her linen till Ostend was taken
• Nichols (1823), quoting 1600 document, and being quoted in OED: rounde gowne of Isabella-colour satten,..set with silver spangles

OK, there's a conflict, so somebody must be wrong. But why assume that it's Disraeli? Could Nichols have misread the original document? Could his printer or OED's have typoed the date? Has anyone checked the original document?

And even if Disraeli is the one mistaken, his story could be basically right, and wrong only in a detail. For example, it might have been some different siege a few years earlier.