i believe the two on the right, are the same as the two front and center in second pic. there are 10 months in between pics
maybe about 5 months ago, i put some them in a q tank to treat for a bacteria(cloudy puffed eye), it reversed it in the blue diamonds for a while, but they started looking bad again and died..
anyway, in the q tank they went non black with the same water. put back in display tank, black again
now and then they aren't black, mostly they are though. just a minute ago the one dropped all black and was full of color over in corner of tank, but by the time i got phone when back to black.
jan 2019
Attachment 125430
nov 2019
Attachment 125431