It is the only decision to make when ordering, and it changes the result more than you would think. Here is how to make it quickly.
Black closes in, white opens up
A black frame acts as a border: it separates the sleeve from its surroundings and concentrates the eye on it. A white frame does the opposite, it lets the image breathe and blends into the wall. With the same content, black gives you an object, white gives you a window.
The rule that almost always works: look at the sleeve
A dark sleeve in a black frame carries on without a break, and the whole thing looks bigger than it is. That covers most rap and metal albums. A light sleeve in a black frame is strongly underlined instead, which shows it off but hardens the wall if you hang several.
White suits light sleeves, pastel illustrations and airy photographs. On a very dark sleeve it creates a sharp outline: that is a choice, not a fault, but it has to be a deliberate one.
What about the wall
On a white or very light wall, both work, and black reads from further away. On a dark wall, on busy wallpaper or on brick, a white frame cuts a clean area around the image, which black does not.
If you hang several prints
Keep the same frame colour across the whole composition. That is what turns unrelated prints into a series. Mixing black and white on one gallery wall is possible, but it needs a regular alternation, otherwise the whole thing looks accidental.
If in doubt
Take black. It goes with almost every sleeve, it reads from a distance, and it is what the large majority of our customers choose.