Word – Removing shading from a text field in Microsoft Word 2016

You can do this, but there are drawbacks:

Method: (with formatting restrictions turned off)

• Insert your content control
• Click "Design Mode" (in the Controls section of the Developer ribbon)
• The default text ("Click here to enter text") can now be edited in any way you want -- with one exception: it must contain at least one character (but it can be a space). You can even change the font face and size.
• Click the "Design Mode" button again, to return to standard mode.

Drawbacks:

• if you remove all the text (save one character), it becomes slightly more challenging for a user to click in the form (a harder target for their mouse). Perhaps you could leave just a few characters, if that doesn't impact your page count.
• if you only use space characters, the content control becomes invisible until you click in it, again, making it more challenging for the user to find it. (Although you can adjust Field Shading to help here)

For more details, refer to this documentation

• Change the highlight colour (Ribbon: Home Tab / grouped under Font / Text Highlight Colour) from white to anything else or No Colour.

• For more information, select part of the text and use Reveal Formatting (CTRL + ALT + SHIFT + S to show the styles pane \ click middle button Style Inspector \ click button Reveal Formatting).