Can you show a screenshot in layout & browse mode? Maybe you can make the leading sub summary, if it contains data you don't need to see, 1 pixel high, or make all the fields invisible, and put a layout object, like a colored block (bar) in the bottom of the header so it stays put.
This cannot be done, but there's no reason why you can't create a single header layout part with two sections in contrasting colors. One simple way to get the second color background is to add a rectangle with a contrasting color to the header and move it to the back behind all other layout parts. You can lock this object to make it easier to move items around on top of it and you can set auto-size anchors that "stretch" this rectangle to fit if the window is resized.