You may have noticed that if you give an image a FontImageSource, the image does not display properly on the UWP platform. This is probably because the default value of the FontImageSource Color property is white, and you probably want to draw it white. Check if you are giving an explicit value to the Color property. If not, try it.
<Image> <Image.Source> <FontImageSource FontFamily="FontIcons" Color="Black" Glyph="?" Size="25" /> </Image.Source> </Image>