I see no grey area, AT ALL. An attack is a violent option, be it with a tooth pick, an axe or a sleep spell.
All attacks cancel invisibility, period. No grey.
I think the grey area involves the E spells. Is Call Cold an attack? You aren't targeting an individual, but you're inflicting a critical on the target. This certainly sounds (to me) like an attack. How about Stun Cloud? Now any victims have the chance to leave the area. So, in many cases you don't inflict damage, but otherwise the spell is no different than Call Cold (now we're in a grey area). How about Aura Burn (causes crits to all that come within some distance of the caster)? The spell just summons some elemental material. How about Bind Fey? It's E so there's no attack roll, but it seems pretty violent. At the other extreme, how about Snake Eyes (causes the target to appear to have slitted eyes)? Doesn't sound like an attack to me. (Unless the target really doesn't want to look all freaky?)
So, if we accept that Call Cold is an attack and Snake Eyes is not, we have to define the dividing line between the two. Personally, rather than trying to choose (and then justify to the players) that line, I've ruled that all E spells are attacks. I suppose you could rule that Call Cold doesn't target anyone specifically, so it's not an attack, but that would make Invisibility too powerful.
My justification: F and E spells involve the caster violently forcing their will on the world. Whereas P spells provide for a RR, the RR only lets the target detect the spell, and besides, the P stands for Passive. I and U spells are a more subtle application of magic than F/E.