Correct Answer: Bright

Solution : The second option is correct.

Dull means not clear, bright, or shiny.

Bright means full of light or shining, making it the appropriate antonym of the given word.

The meanings of the other options are as follows:

• Coloured means having colours, especially as opposed to being black or white.
• Clever is someone who is quick to understand.
• Youthful is someone who has qualities typical of a young person.

Therefore, the correct answer is bright .