Multiple background colours - WORD

First, if you haven't already done so, insert a next page section break, and turn off "Link to Previous" for the header of the second section, as described in my first reply.

For the next step, you'll need a picture with the solid color that you want to use for the first page. You could create it in Paint. It only needs to be very small: it could even be 1 by 1 pixel (but that's hard to manipulate).

Insert the picture into the first section header, then resize and reposition is to fill the page. When you're done, move back to the body of the document. The color picture should sit behind the text.

Insert a next page section break at the end of the cover page. (Page Layout tab of the ribbon > Breaks > Next Page. (If you already had a page break there, you may have to remove that.)

Now go to page 2 and go into the page header. This should automatically activate the Design tab of the ribbon.

Click to unhighlight the Link to Previous button in the Navigation group.

You should now be able to delete the background picture from the second (and subsequent) pages while leaving it on the first page.