Turn over alien, is it red or grey? (6)
I believe the answer is:
mullet
'it red or grey?' is the definition.
The definition suggests a singular noun which matches the answer.
'turn over alien' is the wordplay.
'turn' becomes 'mull' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'over' says to put letters next to each other (in a down clue, some letters go over others).
'alien' becomes 'et' (extra terrestrial).
'mull'+'et'='MULLET'
'is' is the link.
Can you help me to learn more?
(Other definitions for mullet that I've seen before include "Fish (red or grey)" , "Barnet?" , "Starfish" , "Fish - bad haircut" , "Fish, male hairstyle" .)