change background color on one text field

I want to create a form where if a certain condition or field is checked a text box is visible with a warning message which has a different background color than the rest of the form. How can i do this?

Only way to display form warnings inside of your form is to make fields required and then if your user try to submit your form without filling required fields form warnings will be shown.

To make field required select that fields inside of Form Builder and click on required option to turn it ON.

Also you can add hover text to your form fields.

If I did not understood you correctly can you please explain in more details your request and provide us ID of your form.

Hope this will help. Let us know if you need further assistance.