The first combination is one I discovered when I was 13. Surprisingly, it hasn't aged badly, which is impressive given that this was in the early 2010s. I decided that green, black and gold looked really good together. It's not a combination that you see very often so this seemed really new and different to young me.
I think that green, black and gold work because the combination includes a vivid, eye-catching colour (green), a neutral colour (black) and a metallic shade (gold). There's a bit of everything and none of the colours are too close to each other. It's also good for winter because the green matches the evergreens, the dark of the black goes with the bleak weather and the gold adds a touch of sparkle.
You don't see this combination very often. In the UK or US, it is most commonly associated with Christmas and the Marvel Cinematic Universe.
Another combination I like is red, black and gray. While it is often associated with Gothic and alternative subcultures, I think it looks great in any context, from a Halloween costume to something more business casual.
I got started on this one in high school and haven't stopped finding new combinations. It is somewhat common but never fails to be vivid and catch the viewer's eye.
The effect of mostly red with a bit of black and gray is a bright, vivid outfit that is nonetheless defined and grounded
Red, black and gray 'work' because you again have a vivid colour (red), followed by two neutrals (black and gray). Rather than having the sparkle of the previous combination, it provides a more subdued visual combination. This is a good fall or winter combination - fall because the red complements the falling leaves; winter because the black and gray complement the colours of the trees and sky, while the red brings a pop of colour.
The effect of a largely black and gray outfit with a bit of red is that of a cardinal bird in a bush. The effect of mostly red with a bit of black and gray is a bright, vivid outfit that is nonetheless defined and grounded.
Lastly, I love the combination of blue, white and gray. It evokes the look of snowflakes and cloudy skies, and is hence perfect for winter. I have no complicated theory behind this one (though it does follow the 'bright colour plus two neutrals' formula).