Sorry I didn't see this comment right away- I'm happy to answer!!
1. Yes, Fun Computer is infected! The darkness couldn't penetrate their hardware since it was built to be durable/sturdy, so it seeped into their software instead. Since they're not actually corrupted physically, they can't spread the infection like other darkened Sprunkis can. However, they can still aid the other darkened in catching victims.
2. The black in the bonus row is the real Black! The one in the bottom row is supposed to just be a physical representation of the darkness and the way others percieve Black in this universe, but this world's version of Black isn't actually evil; just mischievous and morally grey. The Darkening (phase 2) isn't canon and is an alternate universe where the prophecies that Jevin constantly blabbers about actually came true, but in the canon timeline it never happened, simply because Black didn't feel like it.
3. Okay so! The infection can spread in two ways: either Black manually inflicts it using his powers (which most of the others don't even know he has), or when an infected/darkened Sprunki attacks an uninfected Sprunki. Things like scratching or biting or even just punching can cause the darkness to spread to the victim. Essentially, the infection makes them slowly lose their mind and consciousness altogether, making them a blank husk that wants nothing other than to spread the darkness. The spread of the infection and how quickly it takes over all depends on the individual Sprunki's strength of will. Raddy, for example, is almost entirely infected, but his determination and strength prevent it from fully controlling him. He applied the chains visible on his body to himself willingly, to reduce the risk of him hurting the others. Garnold and Clukr are working on finding a cure, but their constant arguing and difference in moral beliefs has halted their progress a decent bit. They were able to discover that the darkness will clear up very slightly if an infected Sprunki is exposed to light for an extended period of time: they found this out after closing an almost entirely infected Oren in a room with Mr. Sun, whose light was just bright enough to make some of Oren's color return, but not bright enough to make a real difference.