King, hot, with a child mostly in greenish-brown (5)
I believe the answer is:
khaki
'brown' is the definition.
(I have seen 'Yellowish brown ' mean 'khaki' so perhaps 'brown' could also mean 'khaki')
'king hot with a child mostly' is the wordplay.
'king' becomes 'K' (chess abbreviation).
'hot' becomes 'h' (abbreviation eg on taps).
'with' says to put letters next to each other.
'child' becomes 'kid' (synonyms).
'mostly' means to remove the last letter (most but not all of the word).
'kid' with its final letter taken off is 'ki'.
'k'+'h'+'a'+'ki'='KHAKI'
'in greenish' acts as a link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for khaki that I've seen before include "Dull brown colour" , "Olive-drab colour" , "Dark green colour" , "Military clothes" , "Military camouflage colour" .)