What does Shade mean in a solo context? That is an interesting one.
When I think of light and shade in RPGs I think of in terms of good vs evil, lightside vs darkside, and that is where the shades of grey come in.
Now, in a regular game when a player wants to play one of those edgy loners it can destroy a group. The edgy loner is by definition, not a team player.
So is there a place for the edgy loner?
Yes, the solo game is a place where you can play that loner. The oracle makes no distinction between good and evil, villains and vigilantes, heroes and not so heroic figures.
Shades of Grey
If you have that desire to play a character that is not a team player, the solo environment is a great medium for expressing it. Recently I have been dabbling with some more Tarantino/Frank Millar styles. These are both influences that tend to avoid the out and out heroic figure. Combining this with the dark subject matter of the Lovecraftian subject matter and there is great potential for ends justifies the means roleplaying.
My preference still for real heroes, but where the shades of grey come in is the bit part characters I have been jumping into. One was a sorceress responsible for a massacre at an airport, escaping the scene of her crime, another was a petty thief who met a casual and meaningless death. In my case the less than heroic supporting cast simply gives contrast to my own primary character.
When to be evil
If you put your GM hat on and really play your villains to their best potential, the player characters would not stand a chance. The main reason for this is that the villains have years to prepare their plans, years during which they are often ignored and left unhindered. No villain is going to just assume that no one will oppose them, that is non-sensical.
As soon as villains start to take precautions, that is when things get tough. This is the very reason why in the James Bond movies the villain has to capture Bond, bring him into their lair and explain their plans. If they didn’t, they would be very short movies. Villain captures Bond, has him shot, roll credits.
When we play the villain, we end up having to pull them back from their true potential, just to give the characters a chance.
When I encounter a villain in a solo game, I do not pull punches. I let the villain wield the full potential and if they win, it doesn’t matter.
Finding a game to join for a soloist is not a problem, the issue of reintroducing a character to an existing party doesn’t matter, even starting an entirely new adventure to explore another avenue doesn’t matter. Losing to the villains make the victories so much better. The mission or quest may be a failure, but the game can be a huge success. Is the boy from a small town likely to rise up and defeat the demon backed necromancer? Hell no! Can you have fun trying? Of course you can.
Coming back to shades, if you have the urge to bring a loner character to a gaming group, I seriously ask you to consider trying to solo play the character instead. Loners are by definition, not good group characters. They do not add to the enjoyment of the rest of the group, believe me.