If you're looking at Page Layout view and the cursor is in the main body text, then the watermark will always appear dimmed (as will anything in the header or footer). That's by design and can't be changed.
You can see the watermark as it will print either by double-clicking in the header area to open that pane (the watermark is attached to the header), or by clicking File > Print and looking at the print preview on the right side.
If this document is meant to be read on the computer rather than printed, save a version of it as a PDF file and distribute that (File > Save & Send > Create PDF/XPS Document).