If you are using an off white color the complement would be the color opposite of the off white on the color wheel, but it would now be a very neutral blue/violet gray if your off white is a creamy off white. Probably not what you are thinking.

The opposite of BM Paper Mache is pretty close to BM Whisper.

Most off whites look good with a lot of differnt colors.

Many times it is easier to pick a palette from art or textiles that you love or simply starting with one color that you love next to your neutral and building out from there.

It may help if you tell us the neutral and some colors that make your heart sing or share some art that you own and love that we can tie to wall colors. (Often the wall color should be something much softer, more muted than the art, so it works as a backdrop to the art.)