Principal modern paint mixture (11)
I believe the answer is:
predominant
'principal' is the definition.
(thesaurus)
'modern paint mixture' is the wordplay.
'mixture' indicates an anagram.
'modern'+'paint'='modernpaint'
'modernpaint' anagrammed gives 'PREDOMINANT'.
(Other definitions for predominant that I've seen before include "chief" , "prominent" , "Rescue (ship) from loss" , "Providing the main element" , "Influential, controlling" .)