What’s the reason behind washing white clothes in hot water and colored clothes in cold water? I’m under the impression that the hot water helps kill more germs. Is hot water not used on colored clothes because it will cause them to fade more rapidly? If this is so, are our white clothes “cleaner” than our colored clothes?!?!?!
Hot water can cause colors to run, or bleed off on one another; that’s why you wash colors in cold; so your red t-shirt doesn’t come out with blue-jean streaks all over it.
Hot water can be used in the all-white load because there is no dye to run or bleed out.
The goal is to wash your clothes in as hot a temperature and as vigorously as possible without damaging them. So, your white sheets you wash in hot water, but your red shirts you can’t do that. Ditto delicate fabrics, etc.
Because guys don’t like pink underwear 
Speak for yourse-
Er, nevermind.
Washing temperature is both a question about the type of colour and the type of fabric. White cotton, for instance, can tolerate very high temperatures - up to 100 degrees C without disintegrating (cotton is stronger/sturdier when it’s whet). Because of the structure of the fibre and how it reacts to water, you’ll actually need very high temperatures to get cotton really, really clean and white.
The most common dye for cotton reacts at a temperature at about 60 degrees C, so one should be safe if washing coloured cotton at this temperature (it’ll sort of de-react with itself - not the other clothes).
Other kinds of fibres and dyes reacts at different temperatures, and while some dyes can tolerate/need high temperatures, the fibres cannot. For instance wool, can’t tolerate movements very well, as it will tangle and felt. The higher the temperature, the more sensitive it is.
Personally I wash white cotton (blankets, towels, underwear and such) at high temperature. Coloured things are divided into dark, red/yellow and light and washed at medium/low temperature, and wool is washed by itself at the delicate setting and with special detergent.