Merc miniatures have wrong colour tone on bounty map

On a bounty map in Mercenaries, enemy encounters are represented as coins, or nodes, with miniature portraits of the opponents. For most of them, the ‘coin portraits’ are in a sepia (or something like it) colour tone, however, for some mercenaries (so far I’ve spotted it for some versions of Azshara and Vanndar) these are completely greyscale instead, which stands out and is clearly a visual defect.