I'm traveling to Greece (Athens plus Patras and Napfilon) in March. This is my first time traveling to Greece. I've checked on the average temperatures and so forth, but how those temps feel can vary greatly. So I'm not sure what kind of clothing to pack. What should I wear in terms of style and season? I'm in my mid-thirties and traveling with a group of students and college professors. My goal is to look casually professional while maximizing comfort. Any suggestions would be greatly appreciated.

Light layers with thermal undies will cover all your bases.

For outerwear, a rain coat/jacket that looks OK as "regular" outerwear when it's sunny (i.e., none of those easter-egg colors!)... rather khaki, navy etc, that will look good both with jeans, more dressy pants and even w. a dress if that's in the mix. Then some sweaters, not all pullovers ... cardigans are easier to get on/off if it warms a lot. Cashmere is NEVER a mistake.

I like brotherleelove's advice. I like silk for thermals because they dry so quick when you wash them and they're like feathers to pack. You know, you can buy cheap, stylish lightweight clothes in Greece, super easily, so if you are going to err on the side of caution, bring warm knowing you can buy cool.

"Cashmere is NEVER a mistake." LOL! With pearls? Okay- but no twinsets, please!

I couldn't travel with cashmere, especially not if it warms up in Greece. It did on me in the very first week of March a few years back. It was impossible not to sweat -- alot -- in the sun. And cashmere doesn't wash very well if ouzo splashes on it.

Ok, it's coming up to my 4th March living in Greece, so I can definitely tell you to cover all bases! BLL is right with layers! Plenty of stuff you can mix & match.
The only thing I can say for certainty is don't dress for the weather as it is when you go out for the day, 10 mins, 1 hr later, it could be quite different! If I am going out it's a t shirt, then a cardigan or fleece, & take a waterproof jacket &/or umbrella. Sitting in a sheltered spot in the sun can get very warm so the t shirt layer can be useful then, nothing worse than wearing only heavier clothing & you can't cool off. Also you will find some places overheated inside & others with no heating!
Definitely something warmer is needed for the evenings.
Actually this info applies across the board for the winter months, a warm sunny day can happen anytime, I've been sitting in the garden several times over the last few weeks in short sleeved tops, but the last 24 hrs we've had huge hailstones, thunderstorms & gale force winds!
Don't forget a lot of this is relative to what you're used to as well, coming from Alaska you'll think it's warm, from Florida you'll need the warmer clothes more!

Sorry about the cashmere -- but at least I said cardigans. Cardies are all I take, and most of the time they are just tied around my shoulders, after dark, in May.

Thank you, everyone, for your advice! I was contemplating cardigans; now I will definitely include them. The same goes for short-sleeved shirts. Your responses are much appreciated; if you think of anything else, please let me know!

I always wear clothes. Naked will be too cold and might arouse suspicion among the natives. If you're not going naked, short sleeves won't be o.k. in March. It's simply too cold.