I'd just go ahead and say that the Asmodeus was colored green with yellow lights simply because of older design concepts, when all Shivans were going to be green. That much I do know. The lights have been changed to red in the mediaVPs, leading me to call it the Christmas ship. I will some day make a Christmas Tree out of these in FRED, with a sensor array at the top of the tree to take the place of the decorative star. Other ornaments are as of yet undecided.
TBH I think the Asmodeus should now simply have the main hullmetal color changed to black or dark grey (dark grey being SF Mara dark grey) so that its color scheme matches that of the other ships. Surely a color change wouldn't be too OMGWTF on us, it was done with the Cain and Lilith, and this would be one that kindasorta makes sense.
If not, I'd rather the glow be changed back to yellow because red and green do not compliment each other very well unless it is Christmas.
I have absolutely no idea with the coloring of the original Mephisto. The mediaVPs version looks fine, though it could just be my graphics settings.