Which is exactly what I do with them...
The question itself here is flawed -- since even in HTML 4 you have ZERO business saying the color of something in the markup -- that's CSS' job! Problem is no two browsers accept color the same for it, which is why it got to be habit to say color, background-color and border-color all the same to get them to behave.
Though that's a lot of what led people like Ralph and I to set them to display:none and style some other existing element instead... leaving the HR in place for it's semantic purpose of indicating a change in topic without a numbered heading... like say before the page footer. (since it's unlikely the content of the footer is a subsection of the numbered heading tag preceding it).
NONE of the presentational attributes -- size, align, color, bgcolor -- have ANY business being used in markup written after around 2001 (about when we kicked nyetscape 4 to the curb) -- and by the specification should really have stopped using in 1998. It's funny to think back and realize this is exactly WHY IE 5 and 6 became 'the only browsers that mattered' from '98 to around 2003... after all they literally were the most standards compliant browsers of their time!
Though of course one is still writing tranny the above is gibberish -- nothing like being in transition from 1997 to 1998 and failing to grasp the entire point of HTML, the entire point of CSS, and such wonderful and practical concepts as separation of presentation from content, minimalist markup, etc etc... Not exactly a shocker though since this thread starts out as if it's a HTML 5 'change' (it isn't) -- the presence of 15 year out of date markup techniques is hardly a surprise. After all, that seems to be who HTML 5 was created for: the people who never really embraced or understood STRICT, semantic markup, or the dozen other modern coding techniques that result in clean efficiently coded easy to maintain, fully accessible sites.