You know how sometimes old clothes get turned into sleep or lounge wear? I know I have a few old shirts that I toss on when I get comfy for bed... Keeping that train of thought, I assume Samus has taken her alternate costume from her first mission, and has retired it to sleepwear. Sure, her hair isn't green, but that was just a phase she went through when she was younger...

Alternate "Light" version: "Link":http://ronindude.deviantart.com/art/Plushy-Snuggles-Samus-Light-Version-535195512