Beer contains a colouring meant for walls (5)
I believe the answer is:
paint
'colouring meant for walls' is the definition.
I can't tell whether this definition defines the answer.
'beer contains a' is the wordplay.
'beer' becomes 'pint' (beer is typically served by the pint).
'contains' indicates putting letters inside.
'pint' placed around 'a' is 'PAINT'.
Can you help me to learn more?
(Other definitions for paint that I've seen before include "Daub" , "Colouring matter for decoration" , "Use a brush on canvas" , "Decorative coating" , "A pint of liquid decoration" .)