I like to wear a long sleeve button up shirt, roll sleeves up or down, undo or do up buttons, turn collar up against the wind etc, very versatile on warm-in-the-sun-freeze-in-the-shade days. Psychological adjustment helps with cold climbing too - just because you can't feel your fingers doesn't mean they won't work just the same as if they were warm, so don't worry about it and just keep climbing instead of trying to warm them mid-pitch and tiring out. Also don't wear sunglasses even when it's bright - squinting fools you into thinking it is summer