Thanks for all that info , i have reds that do that blue thing too. I have a small net the shrimp like (for some reason), so catching them us easy, i just place it peacefully beside them & they climb right in, so catching is very low stress. I have him in a hang on tank at present, as I've placed him with a couple of girls that have a greenish look about them, to increase the odds if selectively breeding him as best i can to begin with. I have fingers crossed they may produce something that looks a lot like green
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Sometimes the colour drop can be pretty quick, just keep in mind just the process of hunting down and catching the shrimp your after can cause enough stress that the shrimp will drop some colour, depending upon how long it takes to actually catch it and how much chasing it goes through.
I would expect after at least a day you should have a pretty clear indication of which way the colour is going if it changes at all. I would also check the shrimp just after the lights come back on in the tank after a night of darkness. I found ages ago with some of my red cherries at first light in the morning I would see some reds that had gone blue over night but within an hour of the light being on and plants photosynthesising again they had returned to the standard red. I suspect this colour change was due to pH changes that occurred in the tank over night when the plants stopped photosynthesising.
The first test I would attempt with him would be move him to a different tank with possibly different pH and gH but not too extremely different to its current water parameters. This should show you how "stable" its green colouration is, if it keeps the same colouration without turning too yellow or brown then I would say it would be a good candidate for further breeding.