Th difference in speed between the different colour switches is pretty subjective, but there are some fundamental physical differences.
Reds have no click; it's just a clean, smooth travel from top to bottom. The resistance doesn't change from when you first start pressing the key all the way until switch contact is made. They feel faster because of this smooth, all or nothing motion.
To me they felt vague though, and actually "slower" than the others. I tend to press keys down slowly just before I need to, and not knowing when the keypress would be registered was a problem.
Blues are the opposite. There's a slight increase in resistance just before the switch makes contact. Keep pressing and a fairly loud click with a sudden drop in resistance tells you contact is made. There's a bit more travel in the key after that but it doesn't count for anything. You get another click on release as the switch pops back up to meet the underside of the key cap.
I just found them to be too loud. The other issue is if you're holding a key flat down and release slightly, it doesn't break contact. You have to release about 1/3 of the key travel before the switch pops up. Bad for gaming, especially FPS.
Browns are sort of in the middle. You get that slight increase in resistance like blue, but as you push past it and the resistance drops back to normal, you still have to press a tiny bit further to make contact. Kinda like reds with a bump to tell you where you are. If you release even slightly then they disengage immediately. Perfect.
I don't know enough to comment on spring resistance or overall travel distance, apart from black switches basically being heavier sprung versions of Reds.
Here are some gifs to help you picture my descriptions
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