Colour of writing fluid on page (4)
I believe the answer is:
pink
'colour' is the definition.
(I know that pink is a type of colour)
'writing fluid on page' is the wordplay.
'writing fluid' becomes 'ink' (fluid used for writing).
'on' means one lot of letters go next to another.
'page' becomes 'p'.
'ink' put after 'p' is 'PINK'.
'of' acts as a link.
(Other definitions for pink that I've seen before include "stab" , "prick" , "Knock (of engine) - garden flower" , "See 21" , "Flower - make knocking noise (of engine) - cut with zigzag edge" .)