judging by the color of the eye turning black then yes they seem to be breeding colours i have seen this before in one of my mates tanks he had a pair of jade eyes as well and they turned liek a blacky grey and i cant remmeber if its the male or females eyes turn jet black so ye you may have a breeding pair going on mark
i think its either the male or female that gets the dark eyes and dramatically changes im not sure which one but and like u said the other has a slight increase of darkness to the body