Thank her for caring enough to pick out a nice tie for you. Then gently explain to her that while it's a very attractive tie, and you'll gladly wear it during the summer, you hold with those who regard pastel madras as being more appropriate for warm weather wear, than for mid-winter wear. (Just as many women would be uncomfortable carrying a white handbag in mid-winter, you'd be uncomfortable wearing a pastel madras bow tie in mid-winter.) Ask her to help you choose a tie which you'll find more seasonally appropriate.
Unless she's got some weird control issues (have her seek out a trained therapist), this is a rather trivial disagreement. Adults in healthy, stable relationships don't permit "We have differing taste in bow ties," to take on anything like genuine significance. I mean, what's next? A fight over red delicious vs. golden delicious apples? A trial separation due to disagreement over which end of the boiled egg to crack?
It's not like she favors the correct "over the top" orientation of the toilet paper roll, while you stubbornly refuse to abandon your ridiculous "behind the roll" preference. God, people who don't understand why they're wrong about that frankly deserve to live lonely, miserable lives. For sure they won't get invited to any mid-winter ball I'm throwing. I just hate them so much. Well, who wouldn't, I ask you?
Thank You For This.