I have recently been altering my TDS and GH to get them to where I wanted to be on my recently set up tank. It was GH3.5-4 TDS 150, it is now GH4.5 and TDS 160 and the colours are so much better, blue especially, see photo. As JayC says check water parameters and maybe VERY gradually increase GH/TDS (by a one TDS per day at most, is what I did and had no dead shrimp) if it is at the lower end of the recommended parameters. I am a not an expert/professional though! I increased the TDS by adding 1 drop of remineraliser each time (with the remineraliser I use it increases TDS about 25/litre/drop (GH+1/litre/drop), and my tank has 28 litres of water in it.
I saw this nice blue one today, not seen one like this in my tank before. Picture very low quality as it is such a small one at the moment, hope it survives?
Shrimp can loose colour if the water parameters are not right.
You should test all your water parameters now and make sure that they are suited to the shrimp type. The pictured shrimp is a Taiwan bee, so make sure the pH, KH, GH, TDS and Temp are close to their requirements.