Boys in blue (5)
I believe the answer is:
royal
This could be a double definition.
'boys in' is the first definition.
Both the definition and answer are adjectives. Maybe you can see a link between them that I can't see?
'blue' is the second definition.
(royal blue is a kind of blue)
Can you help me to learn more?
(Other definitions for royal that I've seen before include "Wills, perhaps" , "Old gold coin -- stag with 12 or more points" , "Kingly or queenly" , "Member of ruling family" , "Of sovereigns" .)