When text can be added above a hero image using a TinyMce/Wysiwyg, make sure to not choose a color or paste text that has a color in it already. Text that goes over images has a set color of white larger screen widths and green on smaller screen widths. If another color is chosen within the TinyMce, it will override the pre-set colors.
One exception to the color on hero images is the Main Homepage Hero (on the EDU and Portal Homepages). Their text is always white and sits on a green background on smaller screens.