Hand making blue blood turn red? (5,5)
I believe the answer is:
royal flush
'hand' is the definition.
(thesaurus)
'blue blood turn red?' is the wordplay.
'blue blood' becomes 'royal' ('royal' can be a synonym of 'blue blood').
'turn red?' becomes 'flush' ('flush' can be a synonym of 'turn red').
'royal'+'flush'='ROYAL FLUSH'
'making' acts as a link.
(Other definitions for royal flush that I've seen before include "Great hand" , "evidence that monarch occupied throne?" , "Sign of top family's embarrassment" , "Top hand" , "making monarch look embarrassed?" .)