Required fields in an online form are identified only by red colour but the meaning is not explained. What is the problem?

Correct answer: The meaning of the colour may be unclear and inaccessible

The governing concept is accessible visual communication: important information should not depend on colour alone. Some users may not know what red means, may have colour-vision differences, or may use a device where colour is difficult to distinguish. Option D is correct because the form should add a text label, symbol, or instruction. The other choices do not describe the communication or accessibility problem.