Excitedly, Renoir covers girl with some yellow colour (4-4)

'colour' is the definition.
(iron-grey is a kind of colour)

'excitedly renoir covers girl with some yellow' is the wordplay.
'excitedly' is an anagram indicator.
'covers' says to put letters next to each other.
'girl' becomes 'g'.
'with' says to put letters next to each other.
'some' indicates taking the first letters.
The initial letter of 'yellow' is 'y'.
'renoir'+'g'='renoirg'
'renoirg' is an anagram of 'irongre'.
'irongre'+'y'='IRON-GREY'