LW.
The disease is not curable.
Kill it now, and don't risk whatever you have in the aquarium from being contaminated in the future or worse still, killing them.
I would say that the next ones to look out for would be the neons, the will start to show a lack of discolouration, to the point of being almost white.
This is from the scale facing you(and all over the body) are sticking out, and you are looking straight towards the skin.