Yellowed Electronic Toy Water?

[90sfairy]

I have an Aquapet from 2003. The water has gone yellow over the years. A very sickly looking appearance actually. I never kept the toy in the sun, so I'm not sure what happened to it. (it was originally bought by my mum and not bought second-hand). I never played with it much because I think it's really lame (have to be brutally honest here...)
Is it possible to clean out the water and refill it? Or is it doomed?

I took some pictures against something white to show how yellow it has gotten.




about aquapets:
https://www.youtube.com/watch?v=Swz0Ogk1kh0
http://en.wikipedia.org/wiki/Aquapet


Also, the 'pet' isn't broken, it tilts when you tilt it. I wanted to take a picture of it upright against my skin, but that doesn't work well with my ipad camera.