The background of every text is yellow and I just would like to have it normal. It's not highlighted or the text color. The page color option is grey, so I can't click on that. The image is an example of what it looks like. When there is more text, more yellow and the rest of the page is just white like normal, it's just behind the text.
I would say that's a Character Style with a yellow Pattern foreground shading set at about a 30% opacity. It's not a paragraph style because white background is showing between lines. If it was a paragraph style setting the entire block would be yellow.
The line spacing is also sightly more than 1, probably 1.15. If it was set to single spacing the shading would bleed into the space between lines.
Unless a custom VBA routine was used to set a specific RGB value on a custom highlight, the default highlight colors have a lot more vibrance and clarity ... so I'd also rule out it being a highlight.
To verify this, from the Home tab (I assume you are using Office for the Mac 2016 or later) open the Styles pane. The button looks like this:
Select one of the words with this yellow shading and check its Style Name.
Assuming I am correct, then Modify the Style to how you want it to look, OR ... select the entire paragraph(s) of text and change the Style of text to something else, such as Body Text or Normal.