It can be cool, half an hour in the shade (6)
I believe the answer is:
colour
'the shade' is the definition.
(I've seen this before)
'it can be cool half an hour in' is the wordplay.
'it' becomes 'u' (I can't justify this - if you can you should believe this answer much more).
'can be' is an anagram indicator.
'half' indicates taking half.
'an hour' becomes 'hr' ('hr' can be a synonym of 'hour').
'in' means one lot of letters goes inside another.
'hr' cut in half is 'r'.
'cool' anagrammed gives 'colo'.
'colo'+'r'='color'
'u' put within 'color' is 'COLOUR'.
Can you help me to learn more?
(Other definitions for colour that I've seen before include "Quality that results from light reflection" , "Go red" , "Influence" , "Pigment, paint or dye" , "Complexion - pretext" .)