When cast, the spell washes everything in the room with magical power. For the duration of the spell, every object present in the room at the time of casting has a faint magical aura, and is subject to Magic Resistance.
The intention is to make it so that if the Magus were attacked in, say, a bar fight, everything there would become subject to MR, and thus blocked by his Parma, essentially granting him an impenetrable force field.
Based on the Guideline: "taint something with magic".
I'm not sure the pink dot defense is legal. Remember that natural water moved by magic can still touch a magus (just not the force of the magic moving the water). The targets of the spell have not been physically changed in any significant fashion, their substance is natural and their movement is natural. You might get the effect that the taint of magic cannot cross the resistance, but that effectively means nothing.
I was hoping that while a "little pink dot" was slightly abusive to the rules, an actual CrVi effect would be more in keeping with the spirit. Does it actually work, though, or is there something from the rules I missed?
It's very abusive (and also runs counter to the feel of the game), and exactly why the rules were re-written to be more clear.
Only that it's not as cut-and-dried as anyone wishes it was, or at least in definition (if not in concept). Once you try to cite specifics, there's a surprising amount of unexpected grey-scale between the obvious white and black examples.
The pink dot irritates me. I tend to house rule that magic which affects an object but would have no discernible effect should that object interact with an object with magic resistance does not get resisted.
But then again, I'm a Pratchett fan, and that plus the minor hints in canon that magic tends to respond slightly intelligently (being able to delineate between platonic forms, marked targets etc) suggests to me that magic can actively adjust to deal with issues.
Thus, you put a pink dot on a sword, so what? Does that change the platonic form of the sword to be more useful? (or less useful, technically.) No. Thus it does not get resisted. There is no change in the platonic form, it's akin to there being a dot of paint on the blade (which isn't changing the form of the sword, it's an external blemish)
If you put Edge of the Razor on the blade (Or Bluntness of the broken fork (or something like), it's altering the platonic form and essential nature from "Sword" to "Really Sharp Sword" (or "Really Blunt Sword") and thus the magic recognises this change has occurred by magic, and allows magic to resist.
This is actually not much more than a pink dot. If this is how MR works, then a mage could cast EotR on his enemies' swords with no penetration, making them useless against him.
I would suggest houseruling that the magic is stopped, but not the mundane aspects of the target. So if a sword does d+6 and is magicked via EotR (+2) to do d+8, it still does at least d+6 despite any magic resistance. After all, magic or no, it's still a sword.