I judge by what I'm wearing. If I'm wearing a bunch of dark, heavier clothes, I don't think the white bag looks right. But if we have a bout of warm weather and I'm wearing lighter clothes, I'll use my white bags. Yesterday we had some nice weather so I wore my new HH Mercer satchel in chalk.
I live in LA, BTW, so we don't have as much "winter" as most parts of the country.