The main colour when there's a bit of a haze on the river (5)
I believe the answer is:
azure
'the main colour' is the definition.
'azure' can be an answer for 'colour' (azure is a shade of blue). I'm not sure about the 'the main' bit.
'a bit of a haze on the river' is the wordplay.
'a bit of a haze' becomes 'az' (I can't explain this - if you can you should believe this answer much more).
'on' says to put letters next to each other (in a down clue, letters appear on others).
'the river' becomes 'ure' (river in Yorkshire).
'az'+'ure'='AZURE'
'when there's' is the link.
Can you help me to learn more?
(Other definitions for azure that I've seen before include "Heraldic blue" , "A bright sky-blue" , "tone perhaps" , "Deep sky-blue colour" , "Light blue" .)