Darken, as it were, pleasure (7)
I believe the answer is:
delight
I believe this is a double definition.
'darken as it were' is the first definition.
(as in de-light, to remove light)
'pleasure' is the second definition.
('delight' can be a synonym of 'pleasure')
(Other definitions for delight that I've seen before include "Gladden" , "Glee; its spirit rare, Shelley" , "Ecstasy" , "Extreme satisfaction" , "See 5" .)