If I were GM, I would not have allowed this use of silent image.
A figment effect creates a visual illusion of an object or creature. It cannot alter something's appearance. It also certainly cannot duplicate the effect of the third-level spell deeper darkness, which is what you effectively did with this spell!
If you want to use silent image to hide, you could create an illusory object (e.g. a curtain, rock, tree, wall) that you could hide behind.
Also note that your friends would also be affected by the illusion, although you would be able to grant them a +4 bonus on their Will save to disbelieve it by warning them. (i.e. "Hey, I'm going to cast the illusion of a red velvet curtain hanging from the ceiling right here.") Or, they could touch the illusion to automatically see through it, but that might allow your enemies to see you (as a hand sticks through the apparently solid armchair...)
TL;DR: Silent image isn't powerful enough to do what you describe.
Is darkness an object, creature, or force?I don't think it has to be any of those things does it?
Effect: visual figment that cannot extend beyond four 10-ft. cubes + one 10-ft. cube/level (S)
Figment: A figment spell creates a false sensation. Those who perceive the figment perceive the same thing, not their own slightly different versions of the figment. It is not a personalized mental impression. Figments cannot make something seem to be something else. A figment that includes audible effects cannot duplicate intelligible speech unless the spell description specifically says it can. If intelligible speech is possible, it must be in a language you can speak. If you try to duplicate a language you cannot speak, the figment produces gibberish. Likewise, you cannot make a visual copy of something unless you know what it looks like (or copy another sense exactly unless you have experienced it).
I've used silent image this way myself. Some GM's allow it, some don't but by the rules I think it works. A character doesn't normally get a savings throw against the illusion until they study it carefully or interact with it in some fashion. Presumably the interaction reveals the illusion. That's straightforward with a visual illusion of an object that you should be able to touch. If you try and grab it and it isn't there then it's an illusion. If you create an area of illusionary magical darkness then since you wouldn't expect a tactile sensation walking into it shouldn't reveal anything. The only way you should get a savings throw would be to study it carefully. I don't think having darkvision would get an automatic savings throw since there are forms of darkness they can't see through.
Illusion spells can be extremely powerful when used in imaginative ways so I can understand why GM's are hesitant to allow their unfettered use.
Treantmonk talked about illusions in his wizard guide. Since he writes better than I do, I'll quote him...
Illusion Spells and "Interaction": A lot of Illusion spells specifically only allow a save if the illusion is interacted with. This seems faily self-explanitory for something like an illusionary wall. If you touch the wall, you've interacted with it, and therefore get a saving throw. How about if the illusion contains sound? If you make an illusion of a roaring dragon, does hearing the roar constitute interaction? This is when the rules become vague.I'm not aware of any Pathfinder Specific clarification, but Skip Williams did do a clarification for 3.5 that makes a lot of sense, and I would recommend that using Pathfinder, the same guidelines be used. The web article I refer to is located HERE
To sum up, he says that a saving throw for an illusion that requires interaction to provide a saving throw, should require either touching or studying the illusion, and that should, under most circumstances, require an action. So for the Dragon example, if a character is to use a standard action to either study the image, or carefully listen to the roar, or carefully smell the dragon's stench, etc, then a saving throw is recieved. Just hearing the roar by itself however, does not constitute "interaction".
This definition makes sense, and is as close to official as I think we can hope for, so my ratings will assume that your DM uses this criteria. It never hurts to check though, or at least make sure your DM gets a link to the article.
BTW, I don't think silent image is as powereful as deeper darkness simply because it can be so easily disbelieved (If the character thinks to try).
Standing in an illusion is generally sufficient to be considered interaction.
If it's an illusion of something that you could normally touch or feel then I agree.
Sorry - standing in an illusion is enough to be interacting, practically by definition. Anyone with darkvision would also expect to see through it, thus interaction.
Also, as people have said, you can't actually reduce the illumination level, so that means you have to "make inky blackness" as you described. That won't look like magical darkness, so isn't likely to fool viewers (although their Will may be insufficient to disbelieve it entirely).
Regardless of other things, silent image can at least attempt something like this, but you're better off just doing a mist effect instead (more believable for those with darkvision). Will still get a save if you're in it though.
Sorry - standing in an illusion is enough to be interacting, practically by definition. Anyone with darkvision would also expect to see through it, thus interaction.
It's only interacting if there is something amiss for the character to notice.
Darkvision is arguable. If your character enters an area of deeper darkness would their first though be "I disbelieve?". If so then yes, they should get a save.
Also, as people have said, you can't actually reduce the illumination level, so that means you have to "make inky blackness" as you described. That won't look like magical darkness, so isn't likely to fool viewers (although their Will may be insufficient to disbelieve it entirely).
Presumably the caster would make the illusion mimic the effect. An illusion can certainly block light if you believe in it, otherwise you couldn't create opaque objects.
Regardless of other things, silent image can at least attempt something like this, but you're better off just doing a mist effect instead (more believable for those with darkvision). Will still get a save if you're in it though.
Agreed, especially since the mist effect probably would have some tactile sensation that the illusion wouldn't replicate.
I don't think silent image is as powereful as deeper darkness simply because it can be so easily disbelieved (If the character thinks to try).
Actually, there's no such thing as "disbelieving" any more. You must interact before you get a save.
You would be better off creating by creating some sort of fog.
It'll work even better if you shout "Now deal with the Terrible Blue Fog of Damolocles!". Your allies will know you mean illusion and your enemies won't know what to expect except for something blue and foggy.
In the end, illusions are only as powerful as the DM thinks they are.
I don't think silent image is as powereful as deeper darkness simply because it can be so easily disbelieved (If the character thinks to try).Actually, there's no such thing as "disbelieving" any more. You must interact before you get a save.
No, you can study it carefully and get a saving throw without actually interacting with it:
Saving Throws and Illusions (Disbelief): Creatures encountering an illusion usually do not receive saving throws to recognize it as illusory until they study it carefully or interact with it in some fashion.
As for what "study it carefully" means, the designers have clarified that this generally involves a standard action.
Pathfinder is not 3.5. If I were to consider prior editions, we might as well talk about 2E, which made illusionists into terrifying gods. : D