Do you think that it's possible your boss is trying to communicate, albeit passive aggressively, that what you're wearing isn't appropriate? Not seasonally inappropriate but just plain ol' inappropriate? For instance, I'd consider snow boots and coats something that would normally be worn outside exclusively and then replaced with other shoes/garments when indoors, even in a very casual workplace. In the winter perhaps you're given a bit of leeway but in the spring months that style of dress is just so much more conspicuous. I think it's worth asking--especially if you're working with clients at all--"am I attracting this concern because you think I might be ill or because you'd prefer I wear other clothing?" Male bosses are often uncomfortable bringing up issues of wardrobe with female employees because of fear of impropriety. It seems like that's quite possible what at work here.
(PS Solidarity! It's April and I am wearing a very thick, very warm sweater.)
OP here with an update. I had the phrase "It's nice of you to worry, but I don't like being cold." response all set for the next time my boss spoke with me(hadn't seen the "Does my clothing impact on my ability to work?" comment yet.) Which happened last Friday (Friday's are casual days where we can wear jeans). Boss stopped into my office that morning, made a comment asking if I was going to wear my boots during this week. I started with my response only to be cutoff, and then told my boots were unprofessional, and that he expected me to wear more professional shoes in the next week. I was totally taken off guard by this as this is the first time he has said this about my footwear in the 12 years I have been here. Thought it was even more strange that it was said while he was wearing tennis shoes. So I responded with ok, and wore my light fall/spring boots on Monday (required more layers to stay warm and my feet are still chilly.) I included a quote by llehah, because I saw it today and it had a few good points. To answer some points, I do not work with our clients on a face to face basis at all. No clients ever visit our office. The main people I see on a daily basis are my boss, my coworkers, and the occasional delivery driver or fedex delivery guy. My boss does not have a problem talking to the other females in our office about clothing worn to the office (specific coworker who has worn see through white pants with bright colored flower underwear on underneath, to shirts without bras, to shirts exposing bra straps) which I see and agree would be inappropriate for work she she does meet with clients (always offsite at their offices). But I did take in to consideration the part "For instance, I'd consider snow boots and coats something that would normally be worn outside exclusively and then replaced with other shoes/garments when indoors, even in a very casual workplace. In the winter perhaps you're given a bit of leeway but in the spring months that style of dress is just so much more conspicuous." which we are given leeway in the winter not to change shoes (probably has to do with the fact that I spend quite a bit in our offices back areas which at kept at 50 degrees). So this week I haven't had any comments about my current shoes and probably won't here anymore comments about my attire as it keeps warming up hopefully, then I get to close both vents in my office when we switch to air conditioning. So I'm going to keep the phrase "Does my clothing impact on my ability to work?" handy just in case, because I'm still in 3 layers on top in case a comment is forthcoming, and say it for next time.