Or in tardis blue? For this boy's superhero room, the closet door was painted to look like a phone booth! Bat signal over Gotham City behind bed :) this is cute but I think the room should stay with one superhero theme, not superman and also batman.
Union Jacks have been used in design motifs for years. Wether you'd like your rooms to looks a little edgier or more refined, this article explains how to incorporate the the Union Jack into your design schemes. Lots of Pictures for inspiration!