Step 1: Check the form on the published site.

(If you look closely, the text in the "Message" field is white)

Step 2: Open the "Contact Form Content."

Step 3: Go to "Layout" in the settings.

Step 4: Next go to "Field Text" under the "Fields."

Step 5: Then the "Input" tab.

Step 6: Change the font color to white.

 (This may seem counterintuitive, but I promise the process works)

Step 7: After you've set it to white, go back and set it to black again.

(This trick will reset the design so the right color sticks)

Step 8: And voilà!