Terrible danger after green and gold become ordinary (6-2-6)
I believe the answer is:
common-or-garden
'ordinary' is the definition.
(I've seen this before)
'terrible danger after green and gold' is the wordplay.
'terrible' indicates anagramming the letters.
'after' is a charade indicator (letters next to each other).
'green' becomes 'common' (synonyms).
'and' says to put letters next to each other.
'gold' becomes 'or' ('or' is the heraldic name for gold).
'danger' anagrammed gives 'garden'.
'common'+'or'='commonor'
'garden' after 'commonor' is 'COMMON-OR-GARDEN'.
'become' is the link.
(Another definition for common-or-garden that I've seen is " Ordinary".)