Opens pub under railway platform, lovely environment in the shade (6)
I believe the answer is:
purple
'shade' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for purple that I've seen before include "Colour between 14dn and blue" , "Red-blue mixture" , "shade" , "Colour of the angry" , "Red and blue mix" .)