I tried to guess the meaning of the word in bold in the paragraph below using context clues.
I imagined it was referring to something sad and dark. It was opposed to 'the vibrant colors' since it says they offered him no solace. Then it mentioned 'sorrow'.
I checked the dictionary to make sure and it says:
lu·gu·bri·ous
/lo͞oˈɡo͞obrēəs,ləˈɡo͞obrēəs/
adjective