Thank you to everyone for their advice!
Clark's link to the Cleveland Clinic is particularly interesting. I especially recommend that people consult their take on the clinical significance of purple urine.
As for myself, I've been checking the color (though, Sherri, I didn't know the cute song) and keeping an eye on bottle completion all along. However, in the past week I noticed that, while I was drinking about the same (fairly significant) amount of water, the color was staying pretty deep yellow. I was wondering whether I was missing something.
Anyway, I kept drinking water and the color did finally go back to my normal very pale yellow, so I'm happier now.
And, Sherri, you're right, during the winter I do sometimes sort of forget to keep track as carefully.
Be well, Snoopy