Dealing with a colleague who chooses to sit near a window and block light for everyone

This is an answer very specific to germany. It is important you give at least your country in the question, so people can take into account laws and culture of your workplace. Since you didn't, you will have to be the judge of whether German laws and regulations apply to you, or take this as a starting point to inform yourself about your own countries labor laws:

Daylight is mandated. It is not an optional thing. Blocking daylight is possible in situations where the work absolutely requires it (probably no daylight in coal mining night shifts) or it is short durations (the room with the cleaning supplies doesn't have windows) or there are serious measures taken to compensate for it (shorter work time, mental health councelling etc).

This is put into law in

Verordnung über Arbeitsstätten (Arbeitsstättenverordnung - ArbStättV)

English Translation: "Regulation on Workplaces (Workplace Regulation - ArbStättV)"

Link to the online Version in German

If your colleague wants the window blinds closed at all times, have a talk to your manager, whether your colleague needs their own room for some disability you are not privy to, or you need additional protection as required by the law, for example shorter work times for the same money, or if maybe the colleague just needs to be told that daylight is the norm and required by law by management.

This is not an "I like this better" issue. This is an issue of mental health so important that laws about it exist, forcing the employer to make this available.

Your employer has to guarantee this to you. Make them work for their money for once.

Don't confront him any more. You could write an email to your manager explaining the situation. Mention that the consensus for the group is to have the office illuminated with natural light, and that it would be great if a democratic approach could be taken. CC everyone who agrees -- but get their permission before you send it to your manager.

Ask if your manager can speak to the person as a way to avoid further confrontation in the office.

Is there someone he trust and comfortable with that can act as a bridge? Maybe let this trusted person bring up the issue during a light atmosphere, and maybe just have a discussion over sitting environment preferences? Gently tell him about the situation with the office, and be sure there's as little blaming tone (none if possible) when discussing.