Sentence:  Only when the collage had been exhaustively translated into oil , and transformed by this translation , did Cubism become an affair of positive color and <WSD>flat</WSD> , interlocking silhouettes whose legibility and placement created allusions to , if not the illusion of , unmistakable three-dimensional identities . 
Meaning of the word marked with <WSD> tags:  lacking stimulating characteristics; uninteresting