...Visual Appeal: Human beings are highly responsive to visual stimuli. A well-designed form with pleasing colors is likely to capture users' attention and make them more inclined to interact with it.
Personalization: Allowing users to choose their preferred colors gives them a sense of ownership over the form.
Accessibility: Color is not just about aesthetics; it also has implications for accessibility.
https://wordpress.org/plugins/color-picker-for-contact-form-7/