Most interested about colour (4)
I believe the answer is:
tint
'colour' is the definition.
(tint is a kind of colour)
'most interested about' is the wordplay.
'about' indicates a hidden word.
'TINT' is hidden in the letters of 'most interested'.
(Other definitions for tint that I've seen before include "Hair dye" , "'Shade, tone (4)'" , "work for coiffeuse?" , "A slight shade of colour" , "Quality of colour" .)