The nice thing about line patterns is, that parts colored in pure black (RGB(0,0,0)) can be re-colored when used in the drawing.
All other colors are locked and will not change.
There was something with white, but I can't recall what it was.
This in mind, you can now draw in the pattern an elongated rectangle. Set its filling to pure black and its outline to the darkest possible grey so as to mimic a black - e.g. MSOTINT(RGB(0,0,0),5), or RGB(1,0,0).
Now you've got a line pattern, that you cannot only color in yellow, but any color that the RGB range offers.