Give him the Blind keyword and Tremorsense 0
The Blind keyword states that the creature uses special senses to 'see' within a specified range. The quotes are intentional because see is used as a game term here.
The Blinded condition and the many vision-obscuring powers define not seeing something as it having total concealment against you.
You can give him the special sense of Tremorsense (to represent his sense of touch) with a range of 0. This follows the rules of Blind by giving him a special sense but it still keeps the feeling that he can't interact easily with creatures outside of his own square.
The mechanical results of this are:
- All of the characters targets outside of the characters square have total concealment against the character.
- The character is immune to gaze attacks.
- The character cannot be blinded.
- The character always has line of sight to his own square.
- The character is always aware of creatures in his own square.
He does not suffer the following consequences from the Blinded condition:
- Take a -10 to perception checks
- Cannot grant Combat Advantage
- Cannot flank
Note that anybody that has total concealment against him will get Combat Advantage on their attacks. The important point here is that if he can remove the opponents concealment through an ability, then that opponent doesn't get Combat Advantage just because the character is blind.
In uniform, shared light levels, vision penalties due to darkness work fine, intuitively, and exactly as written (no surprises). The deeper the darkness, the more trouble you have seeing, hitting things, and protecting yourself.
This, however, isn't the case you're asking about.
Mixed lighting conditions
Let's stick with RAW to analyse this situation of two people in different lighting conditions. The results are almost entirely the same whether whether Aspartame is in magical darkness or the (possibly very dark) shadow of an oak tree. The results are going to be weird.
These results are pretty counter-intuitive. In real life, the rogue sneaking through the shadows has an advantage on everyone else, and you've probably handled it as such — the rogue themselves isn't blinded by being in the shadows, but they are in Pathfinder!
Pathfinder's vision penalties are counter-intuitive and weird because they don't correctly model vision as we know it: they give you trouble depending on the light level you're standing in, instead of giving you trouble based on the light level of the thing you're looking at. In reality I don't have trouble reading things in the dark because I'm in the dark, I have trouble because those things are.
Like I said though, they work fine when people are sharing the same light levels. They just weren't written with differing lighting conditions in mind and don't handle them well. The sacred RAW should be burned in this case upon the altar of This Could Have Been Written Better For These Cases. Rules are worth the results they produce, and here the results they produce are kinda dumb. Those who wish to apply it exactly because those are the rules can go ahead and suffer the headaches.
Drawing sense out of the ashes.
Pathfinder should probably just be modelling how things really work: darkness affects you based on what you're looking at, not what light level you're in. Accordingly, I'm making a recommendation that in mixed light levels, the RAW be interpreted for what it was probably intended to do — which just requires a small adjustment of the original RAW:
- Dim light: Being in dim light doesn't make you have trouble seeing, but looking at things that are in dim light means you have trouble seeing those things. Past that though the RAW works fine: things in dim light have concealment and you have a 20% miss chance against them.
- Darkness: Being in darkness doesn't make you blind or suffer penalties. However, you are considered blinded for the purposes of observing or interacting with anything that is in the dark. You have a 50% miss chance against those things in combat, you have penalties to AC and perception versus things in darkness, and so on.
- Alternately, stick with the Darkness spell's function, and just grant things in darkness total concealment and forget about blindness.
Wyrmwood brings up in comments that due to firing through concealment, firing past/through dim light introduces a 20% miss chance. This causes sense-making problems if you're on a long archery range, and a tall tree off to the side is casting a shadow across part of the middle of the range: those rules assert your target dummy now has concealment, despite still being in the bright daylight. These rules work fine for actual obstructions like black smoke, but not for light. I suggest that for the purposes of firing through concealment, don't count dim or dark squares — just count what it is you're targeting.
That produces these results, which are probably actually intuitive:
- While Aspartame is in dim light:
- Aspartame is considered as having concealment from Xylitol. Xylitol has trouble seeing him, and has a 20% miss chance.
- Aspartame fires without difficulty, because Xylitol is in bright daylight and clearly visible.
- When Aspartame is in darkness:
- Xylitol is considered as being blinded for the purposes of trying to observe Aspartame. He has a 50% miss chance trying to attack Aspartame.
- Aspartame still fires without difficulty, because Xylitol is in bright daylight and clearly visible.
- Xylitol has all the defensive and sensory penalties for the purposes of any interaction between himself and Aspartame, because he can't see what Aspartame is doing at all.
We get these results, again, whether the dim light or darkness is due to magic or the shade of an oak tree.
Best Answer
Yes, you are always allowed a save
Even an unconcious character should be allowed a saving throw, regardless of their state. The fact that he is blind does not change how well he can protect his body against harm. Reflex saves are not only movement (dexterity), but also about luck (the dice roll) and training (the class bonus).
But since he does lose his dexterity to AC, a GM could rule that he also takes a penalty on his Reflex save, but that is a house rule and is up to the GM.
If the GM denies that character a Reflex save, then he will have some explaining to do when the rules say that a paralyzed (or unconcious) character are allowed to make Reflex checks with a -5 penalty but his character can't.