The outside air at cruise altitude is always extremely cold regardless of the season, so the amount recirculated won't change significantly (if at all). As WillCAD notes, it's simply a matter of being surrounded by more sick people.

(Media myths about recirculated air on airlines is one of Patrick Smith's favorite pet peeves - here's one of his interesting articles on the subject.)

Also, I think it's pretty rare to catch colds from viruses that are floating through the air - much more likely that you've touched a tray table, IFE touchscreen, seat back, or other item that's been in contact with a sick person.