It is depending on the situation.

I you are on a more formal Business trip and do not have any leisure time, you should leave the Jeans at home. As written by previous posters, in winter you wear more dark coloured clothes than in Spring or Summer. The other side, especially in Winter and rainy / snowy weather conditions dark pants have some advantage as they do not get dirty as fast a beige pants. And the clothes should be warm, especially Berlin could be really cold in January and February.

Shirt with tie and dark blazer should be okay for business. The IT business is a little bit more casual, while the financial business it more formal dressed. Government people dress formal, at least if they have a meeting.

If you have some leisure time, Jeans / Khakis and shirt (without tie) or turtle neck are okay.

Living in Germany, I have had not problem to enter a bar or restaurant in a upscale hotel like Intercontinental, Westin, Kempinski etc. in Jeans with shirt.

And it is depending on the age. Younger people dress a little bit more modern while elder people stick with dark colours and white shirt with tie.