Depends on how cool (cold) it is, with some variation depending on how well you tolerate the cold. For example I tend to have problems with cold feet so I wear warmer tights than many other people do under the same conditions.
That being said, you can find cycling capris with a chamois (padding). They're good for spring and fall temperatures. You can also buy knee warmers or leg warmers that you wear with regular bike shorts.
For colder weather, you can get tights with or without a chamois. The ones without a chamois are typically worn over regular bike shorts. The benefit to them is that you can wear them more than once between washings and can also wear them for other activities. I wear my winter bike tights (without a chamois) for walking to the gym, shoveling snow and on really cold days, just hanging around the house.
For colder weather you will typically also want something to cover your shoes -- toe covers (to cover the front half of your foot) or booties that cover the whole shoe. Tights and booties come in different thicknesses/levels of fleeciness/wind protection so some are better for very cold temps and others are comfortable on days that are just chilly. Again, it's a somewhat personal thing -- I will wear booties when most other people are fine with just toe covers.
If you click the "Shop" link at the top of the forum page, you can see that Team Estrogen sells a variety of capris, tights, toe covers and booties, so you can see some of the different brands and varieties. They also have jackets, base layers, caps, gloves, everything you could possibly need.
- Gray 2010 carbon WSD road bike, Rivet Independence saddle
- Red hardtail 26" aluminum mountain bike, Bontrager Evoke WSD saddle
- Royal blue 2018 aluminum gravel bike, Rivet Pearl saddle
Gone but not forgotten:
- Silver 2003 aluminum road bike
- Two awesome worn out Juliana saddles