Since it appears your 'Heading 1' Style starts on a new page, insert a 'Next Page' Section break before it and configure the Section on which it starts with a 'Different first page' layout. You can then insert a coloured rectangle into the page header, centred and positioned at the top of the page, with text wrapping set to 'behind text. Provided you make it high enough, it'll come down behind the Heading 1. It doesn't have to come all the way down to the bottom the the 'Heading 1' paragraph - pehaps just half way down the first line - you can shade the 'Heading 1' Style also so that correctly it finishes off the shaded range (especially useful if some of the headings span more than one line.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]