Jealous of My Son's Colour-In Pyjamas

Son pester-powered me into buying these M&S colour in pyjamas. They are in the sale for £7, and comprise of a t-shirt and shorts. Both pieces could easily be worn as daytime attire too. The ink washes out each time you wash the set, and although it says you can wash with other colours, I think I'd be playing it safe and washing the set on it's own.