If an input error is detected, the item that is in error should be identified, and the error should be described to the user in text. This doesn't mean that it can't also be denoted by color or images, but a text explanation of the error needs to be provided.

Offical Requirements:

3.3.1 Error Identification: If an input error is automatically detected, the item that is in error is identified and the error is described to the user in text.

How to fix:

• Provide error notification text to notify the user that something is wrong. thsi can be done either client-side or server-side
• On form submission, change the label text of fields that are in error to indicate the nature of the error.