8 pcs Asian Exfoliating Bath Washcloth - Red & Green

When bathing, what is the most effective routine when using these washcloths? Is it better used while bathing/showering, or after?

Can these be washed in the washing machine?

Says to use after soaking in tub to loosen skin, but I only have a shower! Still ok to use?

Just to clarify, red is the least abrasive, green is medium and yellow is the roughest? This is a statement, but I had to place it in the form of?