What effect does adding too much black have on poster colour?

Correct answer: The colour may become heavy and dull

The governing concept is colour modification by mixing. Black has a very strong tinting effect and lowers the perceived value and brightness of another colour. If too much black is added, the original hue can lose its freshness and appear heavy, muddy, or dull. It does not make the mixture brighter, transparent, or white. For a controlled shade, black should be introduced in a very small amount and tested gradually. Therefore, option B is correct.