Kind of a weird question from a newb :)

I understand that if I submit a skin and it gets used, it can't be removed from the game and the game owns it, in a sense. I also get that I can't sell that skin or submit it elsewhere. 

But, does that also go for all recolors based on that lineart? Obviously we're talking of a case where I've made my own lineart/base instead of using the game's PSDs. 

For example, if I submit say, a tiger striped unicorn, and it gets accepted, can I still use that lineart to create differently colored character art, etc?

The short answer is yes, you can do this.

By submitting a custom skin you agree to transfer the copyright for a specific image. Though we get the right for derivatives of this specific image, we don't get any rights for preliminary works and their derivatives. Just make sure that if you're going to sell these derivatives to another person or company, they are fine with getting the artworks that are based on the same lineart. For example, some other pet browser games require the art to be 100% unique and created from scratch.

Thanks for the info, Angel! 

I'm not really looking to sell the images off-site. I just thought that, after making the shared skins, I might make a few custom ones, or I might make a character sheet for myself and a few others.