Start to understand in the man's colour (3)
I believe the answer is:
hue
'colour' is the definition.
(I know that hue is a type of colour)
'start to understand in the man's' is the wordplay.
'start to' indicates taking the first letters.
'in' indicates putting letters inside.
'the man' becomes 'he' (pronoun for a man).
The first letter of 'understand' is 'u'.
'u' put inside 'he' is 'HUE'.
(Other definitions for hue that I've seen before include "Shade of colour; Vietnam port" , "complexion" , "Delicate shade" , "'Pigment, colour (3)'" , "General outburst of alarm or protest - . . . and cry" .)