By virtue of being fighting man, following a colour (10)
I believe the answer is:
aquamarine
'colour' is the definition.
(I know that aquamarine is a colour)
'by virtue of being fighting man following a' is the wordplay.
'by virtue of being' becomes 'qua' (Latin word meaning 'in the capacity of' or 'as').
'fighting man' becomes 'marine' (member of the Royal Marines).
'following' means one lot of letters go next to another.
'qua'+'marine'='quamarine'
'quamarine' after 'a' is 'AQUAMARINE'.
(Other definitions for aquamarine that I've seen before include "Beryl" , "Bluish-green colour" , "Pale bluish-green" , "Greenish blue" , "Gem" .)