good suggestion! technically doable too, and it would fit the site graphic style better..
..but it made me think. say, there's 19 colours (hatchable + dyes) per pet. three ages, and all have their own derp image. 55 creatu, minus 10 that kirby mentioned had already transparent bg..
45 creatu x 19 colours x 3 ages
... 2565 images.
that's a lot of saving and re-uploading imho. so while the operation is technically simple, just take the background off, but even a suggestion simple as that will take a quite bit of work 8U
so while im 5/5 up for this suggestion, its prolly gonna take a while!