This particular magical advantage seems to be linked to places with higher than average levels of interdimensional travel. Basically, it’s an occult mutation of the rods and cones of the human eye that allows someone with this advantage ‘see’ Gates – more specifically, it allows them to see the lingering radiation that’s produced as a by-product from the imposition of a Gate (magical or otherwise) onto the landscape. The ability only works in areas of low mana and above, and anybody with Tetrachromancy is already a mage, albeit a very basic one.
Naturally, most interdimensional organizations get very nervous about hidden individuals with Tetrachromancy. Fortunately for those organizations, the range for this advantage is significantly shorter than line-of-sight. For that matter, a trained and loyal Tetrachromancer can be very handy in the field…
This advantage was bought as a combination of Magery 0  and See Invisible [Gate Residue] , with the Magical [-10%] and Reduced Range [-10%] limitations placed on See Invisible [-3].
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