Antonym of shrewd: stupid, blunt, foolish, ignorant, slow, unclever, unwise (those are some)
Antonym of confident: depressed, sad, unsure, weak, afraid, cowardly, doubtful (those are some)
Antonym of drab: bright, clear, good, light, pleasant, clean, cheerful, happy, (those are some)
Antonym of articulate: inarticulate