I noticed that the color mapping in the API for some of the guild tabard background colors seems to be slightly incorrect for certain background colors.
I have had to remap these background colors (as retrieved from the guild API) so that they show the correct background color for the tabards:
Front end does have their own color mappings that don't match what's in the database for these guild emblems. I will ping them and the game team and see if I can get the correct values added to the API.