Neat concept, but I don't quite get the flavor with exiling and casting from exile.
I think the line about casting from exile should go after the effect that exiles, though. It's strange to read in its current form.
I've noticed a discoloration on old cards as well. I'm pretty sure it's just due to age and not due to being fake. I don't think anyone would make fake whitebordered lightning bolts anyways.
Negate is targeting the spell. Negate counters the spell that you select as its target (as long as it isn't a creature) it doesn't just counter a spell that targets something else.
So yes, you can use negate to counter an enchantment, although, enchantments do actually target when they're cast. I mean, auras target, not just regular enchantments.
There was a dude on another site that had a very similar problem. It really doesn't look like there's a good way of solving the problem you have. Very interesting question, though. Made me get an account just to reply.
I think the line about casting from exile should go after the effect that exiles, though. It's strange to read in its current form.
So yes, you can use negate to counter an enchantment,
although, enchantments do actually target when they're cast.I mean, auras target, not just regular enchantments.