Is Mr Color enamel or acrylic.If enamel,you need to protect it with an acrylic clear overcoat,then you may use enamel or oils for wash.
If is is acrylic,then it standup to oils or enamels on its own,just no acrylic washes.
If you mix your own,it's usually 90-10% thinner to paint
Many companies make premixed: Mig Productions,Mig Ammo,AK are some that come to mind.