Partially Exclusive

Partially Exclusive is a limitation found on PP17 for See Invisible.
It's -20% pricing gives certain implications when trying to model the limitation under existing rules.
The "dark muted gray" giving -4 to "all Vision rolls" is presumably only meant to mean vision rolls for non-invisible things since the "real world" is what looks like that.
*weirdly this should actually give some kind of benefit to spotting invisible things, since they would be bright non-muted non-gray and stand out better, but this isn't mentioned anywhere
Since Completely Exclusive implies that See Invisible is already switchable by default, the -20% limitation could be used to guess what sort of Temporary Disadvantage(s) underlie this limitation.
==Bad Sight==
It does not fit either form of Bad Sight in Basic Set.
*B144 Night Blindness by comparison is only -10 and makes you -3 at -1, -4 at -2, -6 at -3, -8 at -4 or completely blind at -5
Low Resolution from Toolkit 2 by comparison gives "‑4 to spot objects at any range" as a 25 point disadvantage, which is closer to how PE works.
PE lacks "-8 to resolve fine details" which might explain why it's only -20% instead of -25%
==Buydown approach==
B16 allows buying down Perception at -5 points per -1, so it would be -20 to lower it by 4 points (this is the maximum allowed without GM permission).
If ALL perception (every sense, including vision rolls to visible and invisible alike) suffered a -4 penalty then this would warrant -20% limitation.
Limiting it to JUST vision would presumably be worth FEWER points.
Buying back all normal Per rolls EXCEPT vision isn't a workable approach, because the total of even the 3 listed ones (taste/smell, touch and hearing) is 6/level.
Pg 4 of Enhanced Senses mentions "Acute Senses, which amount to discounted forms of Per for one sense each"
Shifting the cost of 5/level to 2/level essentially prices "One Sense Only" on Per as being a -60% limitation.
B46 this is the same as Limited Defenses to an Occasional threat (B34) which has a -5% value for Bane.
*this indicates Per (all senses except 1) is actually not enough to get a discount on a single point: to save 1 point with -5% something needs to be worth at least 20 points, which is 4 levels of Perception.
**ie Perception+4 (Bane: Vision -5%) [19].
***if you take this with Perception-4 [-20] then the net metatrait "-4 to Vision rolls" is only a QUIRK, meaning worth merely -1% as a Temporary Disadvantage
==Colleges approach==
T42 under One-College Magery With Variant Colleges suggests that -60% represents "more than 30".
Taking that interpretation for the -60% based into Enhanced Senses establishes "more than 30" senses are assumed as possibilities.
:"If the GM allows the Limited Colleges limitation (p. 25), then he should scale it proportionally"
This indicates that the +10%/college is scaled for the default pricing of -40% (15 to 30 colleges) introduced on B67.
*this is a 1/4 increment, so it should be 50% more (15% increments) for 60%
Instead of "One Sense -60%" you could have:
*Two Senses -45%
*Three Senses -30%
*Four Senses -15%
*Five Senses -0%
There would be no point in buying "Five Sense Perception" as it would not be cheaper, just like there is no benefit to buying "Five College magery" in a -40% setting where there are 15-30 colleges.
*though what you could do is take Alternative Abilities of different kinds of magery which can give more versatility and lower prices
==PU4==
Pg 11's Modifying Other Characteristics in the Wesley example does not use Reciprocal Advantages to determine value of enhancements.
For example to add Link to hearing and vision:
:+20% "if he hears something, he doesn’t have to make a second roll to see it, and vice-versa"
:+10% "force Wesley to look at what he was hearing" (presumably would also force someone to hear whatever they looked at if hearing had Selective Effect or Parabolic Hearing)
These are not applied to Not Blind [50] or Not Deaf [20]
*Instead they are applied to Acute Vision 12 [24] and Acute Hearing 13 [26]
This made his vision cheaper to modify and his hearing more expensive to modify.
It is possible to take the Shutdown variant of Temporary disadvantage where you remove an ability, rather than add an advantage.
If using THAT approach, removing 4 levels of a 2-point advantage (acute sight) should still only be -8%, not -20%.
*an 8% discount on 15 only saves 1 point, not 3
Clearly this can't be solved by just doing a % discount on SI's 15 points because the discount is too slim. 
==Alternative Acute Sight approach==
Acute Vision 4 is normally 8 points.
*vision has Affects Insubstantial +40% (B102) built into it
**so Insubstantial Only vision bonuses 
Alternative Abilities (1/5 cost) makes alternative Acute Vision 4 worth 1.6 points.
The point difference (points lost) in reducing that many points of Acute Vision is 6.4 points.
==GMEP==
Reverse-engineeering generic minor eyesight problem is another approach.
1 second of focus removing a "-1 to vision" disadvantage being worth a quirk by itself argues against "always -4 to vision" being -1 via the "buydown" approach of Per which doesn't apply to vision being merely -5%.
category:limitations