Toasted William the Just! (5)
I believe the answer is:
brown
'just' is the definition.
Both the answer and definition are adjectives. Perhaps you can see a link between them that I can't see?
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for brown that I've seen before include "Colour (of the PM?)" , "Rugby hero" , "Kind of sweetener" , "Four-point ball" , "Colour of earth" .)