It depends on how you define "cold." And also depends on how well you deal in general with cold weather -- some people feel the cold more than others so they need more layers. And everyone seems to have their weak spot that stays cold when the rest of you is comfortable. For example some people struggle with cold feet (that would be me) or cold hands or they start wearing balaclavas to cover their faces as soon as the temperature goes below 55.
Here is one very recent thread that gives good information.
There are also some good old threads on dressing for winter cycling -- search on "cold" or "winter" to see some.
- Gray Trek Madone 4.7 road bike, mystery crack in top tube repaired by Calfee, Bontrager Affinity RXL saddle
- Red Trek 6000 mountain bike, Bontrager Evoke WSD saddle
Gone but not forgotten:
- Silver Trek 2000 road bike
- Two awesome and worn out Juliana saddles