Glofish tetra turning blue?!

Title says it all. My teacher and I got a 20 tank set up and after a week and a half when we did a water change I noticed the heads on some of the tetras were turning a blue color and there's no blue glofish tetras in that tank at all the pink and green ones showed this weird coloring. We have no idea what happened. Genetic mixing while breeding shouldn't be a cause because the blue doesn't look like it glows. Anyone have an idea what it could be? There's 6 glofish tetras on the 20 gallon and 3 zebra danios were removed during the water change because they were too quick and took all the food. Bullying wouldn't explain the blue most likely because there's one green bully that only messes with the other green tetras and the yellow on occasion but there's also a really big pink tetra that doesn't care and isn't bullied by anyone but still has a blue head

 

Do you have a blue light on? Try a regular light and see if it's a white spot.

 

They were originally created to monitor water pollution. I'm not sure how that works, Mabee there color changes some under poor water conditions. You may also have one that was born of 2 different color glowfish. I know my pink one brightens up after I do a water change.

 

They were originally created to monitor water pollution. I'm not sure how that works, Mabee there color changes some under poor water conditions. You may also have one that was born of 2 different color glowfish. I know my pink one brightens up after I do a water change.

The danios were, the tetras weren't.

 

The danios were, the tetras weren't.

Really I had that backwards? Thanks lol