Could almost be any colour. Originally in black. Would make most sense in green (enemy of black discard and blue reveal) or white, but they don't like 3/1 as much. Decided "any colour but black" was right place, and 3/1 sounded red.

Undecided whether if opponent plays a "look at hand and discard" spell they should have a chance to discard this or not.

At the moment they don't. Which differentiates it from Wilt-Leaf Liege, Dodecapod, and suchlike, at least.

Are you sure? Isn't this a triggered ability, making the discard resolve before the triggered ability resolves, and then the triggered ability doesn't (?) let you cast the card from the graveyard?

But I agree it doesn't matter much, and could easily be worded either way: either way, it triggers sooner, and by the time the opponent's seen it it's probably too late, since they have to get rid of it rather than a bigger threat, or let it come into play.

Er... When I said "they don't", I meant "this doesn't"... as in "they do". Ahem :) For precisely the reason you state, yes.

Ah, oops, I see. Nevermind :)