The pink background on a text indicates that the font is not available on your system. The problem may occur when you have selected a font for example "Times New Roman"/Bold and then you have changed the font for example "Adobe Garamond" then the pink background appears, because this font family does not have a bold style typeface, so you have to change it and the pink background will disappear. You will see in the style menu like this [Bold] every time the font family does not support that style it will appear like this.