If grey appears greenish after adding yellow, what is a likely reason?

Correct answer: The grey already had a blue bias

The governing concept is hidden pigment bias in a neutral mixture. If the grey contains a slight blue bias, adding yellow places blue and yellow together, producing a greenish visual tendency. This does not mean that yellow is always green; the result depends on the colours already present. A red bias would tend to counter green, and excess white mainly lightens and weakens the mixture. Therefore, option B is correct.