Royal blue can look cheap, it is a very common colour for cheap market stall blouses and jumpers in my youth.
On the right person it looks stunning, I had a black African flat mate who looked stunning in her royle blue bridesmaids/ ball dress (her sister let her choose one for both).
My auburn haired DD has a Sainsbury's coat that colour and looks lovely in it.
Me, I'm a mousy brunette and I look like I've spent 50p on my clothes if I wear royal blue.