So the issue was identified. Those portraits are saved in 'Grayscale' mode and FGU does not currently support that for PNG images. If someone wants to update those via Gimp or similar to save them in "RGB" mode then they will work correctly.
Moon has created an issue to track this for resolution, but as you can imagine, it's low priority. https://www.fantasygrounds.com/forum...l=1#post542075