Depending on the choice of the font color in the header and color of the header itself, certain themes can't display the reports correctly. The issue arises, for instance, if a dark theme is chosen with white font, or in general if the value of the chosen color is close the color of the surrounding box.

This patch takes in account the theme colors, interpolates between them and finally uses the grayscale to apply to the surrounding box. This should produce more legible report in more different theme combinations.