Who are Red and Blu (for aesthetic purposes)?

Hi, there.

I've started porting a HL2dm map into TF2 recently, and I'm converting the theme into TF2's default desert-ish style, with farms, spytechs, etc. I've been observing several maps to gather how structures are made, and layouts, etc, and I've already made a few nice modifications. However, I'm afraid I may run into a few misconceptions along the way. The biggest of which is my uncertainty about what exactly are Red and Blu?

I know from 2fort that Red are farmers, and I assume from Sawmill that maybe both teams are woodcutters. I have this feeling that Blu deals with factories. But I'd like to have a more in depth certainty of it all, since this will perhaps help me decide what buildings to fill the map with.

So, if anyone can help me on this, what exactly are they, and what do they do?

Any other tips you may think of will be appreciated. Thanks.

Thanks for all the great answers. I had noticed a few things, the facade reason of it all, like Sergis stated, and the wooden houses for RED and concrete structures for BLU construction "habits". Though I didn't notice most of the details. Valve created quite some depth in them, indeed.

I've been looking at the signs textures in hammer and I found them quite useful as hints.

I still think I need to learn how to replicate the structures though, as they both tend to be quite complicated. I don't know if there's any useful patterns...