Ooops, I forgot about Ogrins.
Well, I wasn't going to give my answer, but I'd better say now that another answer's been revealed.
I put orange, because you can get orange pteris:
BOTH answers seem reasonable:
- Ogrin:
all the others are pets.
- orange:
(a) the fact that all the others (barring Ps) are pets is irrelevant -- this is about the lab ray
(b) because it's a small o:
The
Discarded
Magical
Blue
Grundo
Plushie
of
Prosperity.
Personally I think the answer's going to be Ogrin, but I sincerely hope that TNT either accept the logic of the small 'o', or allow both answers.