Yellow Watchman Gobies that aren't so yellow

[Calm Blue Ocean]

I'm looking for some insight into YWG coloring. I've seen it suggested that it is an indicator of male vs female but apparently this isn't necessarily true either? I'd be less curious if my YWGs maintained a color through their lives but this has not been the case.

This first picture was taken not long after I got these guys. They were sold as bonded pair. Cute little tikes and most definitely both yellow.

This picture was just over a year later. It's not hard to tell them apart anymore! They never spawned and I don't honestly know which was male and which was female.

Back at the beginning of April we lost the yellow colored goby. And now the silver one seems to be turning back to yellow! (ignore the wrasse face in the back, I just did a water change and she's still hiding)

So both gobies started yellow. Over time, one turned silver. Lost the yellow one, and now silver one is turning yellow again!

Does it mean anything? No idea. At the very least, it's mildly interesting!

 

[Sump Crab]

I bought mine as yellow and it lived that way for several years. At one point it turned grayish and has never gone back to yellow. Its 12 years old now.

 

[ying yang]

Bought one about 3 weeks ago and as lfs guy pulled it from under the sand in a burrow with a pistol shrimp it looked more white than yellow.the guy said as it gets older will get more yellow.
As soon as got home and put in tank it was yellow lol.
I just thought was stress induced from being caught why it was white at lfs as some fish lose
Colour when stressed but idk