Discoloured fish

I’ve just come home from a 7 day holiday where I left a member of the family with portions of food I set out beforehand and he came up and fed them everyday. I even set up a camera and my fish seemed fine. I got home and it was around 12:40 am and obviously the tank lights were off. (40 mins past midnight not midday) I put my torch on to see if everything was alright (I.e the temperature, to see if the heaters had done their jobs) and I noticed a Baggai Cardinalfish (Who normally had three dark black stripes down him) who’s black stripes had turned white and was sort of resting on the floor upright. The other cardinal was acting similarly but had more black colour in his stripes. I then noticed my azure damsel’s Blue half was very light and sort of white too and he was coming out because of my torch. The fish then started to colour back to their normal selves a bit more and I have since decided to leave them alone but I was really worried that they were ill? Is this just something fish do at night? Go quite pale? As I say, when the light came they started to turn more colourful again. Ammonia:0 nitrite:0 SG:1.025 temp:25 degrees C

Thanks for the help.