A family of Microsoft word processing software products for creating web, email, and print documents.
Word does not make it possible to change the page color for only one page. That function always changes all the pages. However, there is a workaround.
First insert a next-page section break (Layout > Breaks > Next Page) at the end of the third page, and another section break at the end of the fourth page.
Double-click in the header of the fourth page to open the header pane. Click the Header & Footer >Link to Previous button to turn it off. Click the Next button on the same ribbon to go to the header of the fifth page, and click Link to Previous to turn it off there too. Then click the Previous button to return to the header of the fourth page.
While the cursor is in the header of the fourth page, click Insert > Shapes. Choose the rectangle tool. Click and drag the mouse to draw a rectangle on the page, and drag its sides, top, and bottom until it covers the entire page. Click Shape Format > Shape Fill and choose the color that you want for the page.
Finally, click Header & Footer > Close Header and Footer. The rectangle's color will be more pale than the color you picked, because Word always fades everything in headers and footers in the Print Layout view. To see what the page will be if you print the document (on paper or to PDF), look at the preview in the File > Print view.