This is partially because people wear less white and partially because our detergents and dyes no longer leach colour out of clothing. The dyes are more fast, and the detergents are less harsh.

I've posted about this before, but you should be separating based on fabric weight and elasticity, not colour.

Things you want to stay elastic: Don't use softener, use cold water.

Things without elastic: You can use softener if you want, use cold water.

Literally there's no reason to use hot water anymore, washing machines and detergents don't need that help any longer unless you're specifically dealing with grease/oil.

DON'T put bras or elastic in the dryer. That instantly destroys them, it's like putting them directly into the garbage. Bras are dangerous to wear after being in the dryer, they will fuck you up nine different ways please hang them up.

(I know many folks don't use softener but those little dryer sheets count)

I only wash towels and my bedsheets/pillowcases in hot water these days. Maybe it's placebo but I swear my skin breaks out less that way.

sheets are full of oils from your skin so it's very good to wash them in hot water! Hot water is very good for oil. However, if you ever have blood on your sheets, rub ice on it, use peroxide, and wash it very cold or you'll set the blood (iron is a powerful dye!)