I'm curious as to why she is so concerned about your hair. If she starts in again the next time you see her I would ask her why and make her explain herself.
Or you could simply say you joined Going Gray Looking Great.

I love that, Linn.

"Wow, you seem to be REALLY interested in my hair. What's up with THAT?"

Thanks, everyone! MaryK, I really like that 'reframing' idea! Think Im going to try that on my sister too..she drives me up the wall most every day Great comments too....Michelle, I think you read my mind with your first reaction! Exactly what I thought....great idea that you had too....San, I definitely will try that, thanks! Linn & MaryK, I think what really bugs here is that when she first began working there (I had already been there several yrs) she had medium brown hair and after a few months, she dyed her hair red, in a shade very similar to mine...she kept it that way for several yrs and now is letting her grey show a lot more than it ever did and I think it bugs the heck out of her she's a *lot* more grey (about 40%) and I am about 10-15% so she feels compelled to point out mine..aaggh You all have been SO great helping me deal with this! I truly appreciate it

I'm sorry but someone with a rude comment, should just be slapped. I'd have said, "thanks for noticing" and left them feeling awkward without a further discussion of their chosen topic.