Pale colour of engineer working to contain loch (4,5)
I believe the answer is:
nile green
'pale colour' is the definition.
(I've seen this before)
'engineer working to contain loch' is the wordplay.
'working' indicates an anagram.
'to contain' means one lot of letters goes inside another.
'loch' becomes 'l'.
'engineer' anagrammed gives 'niegreen'.
'niegreen' enclosing 'l' is 'NILE GREEN'.
'of' is the link.
(Other definitions for nile green that I've seen before include "Pale colour" , "Pale shade" .)