In premultiplied alpha, you can think of all the legal (non-emissive) colors as a triangle. At an alpha of 1, all colors are legal, tapering off as alpha decre

In premultiplied alpha, you can think of all the legal (non-emissive) colors as a triangle. At an alpha of 1, all colors are legal, tapering off as alpha decreases until you reach an alpha of 0, where no colors are legal. To turn the triangle into a square, you could scale it up by two, cut off the top, and rotate the top over into the empty space (like this: https://i.imgur.com/6hjNe7X.png https://i.imgur.com/6hjNe7X.png). That would give you twice the colors you had before.