What do you call "negative" paint?
I think what you are looking for is called a masking fluid. It is sometimes also called liquid frisket.

Masking fluid can be treated like paint which wherever it is applied will protect what is underneath. A feature of most masking fluids is that they are removable once dry.

Some masking fluids are strongly hydrophobic (water repellent), and water will bead on its surface. This can make it tricky to tell when the whole canvas is dry. Trying to remove the masking fluid but having some undried paint pooling on the surface can cause heartbreaking smears.

Some masking liquids change colour after they dry. This makes it easier to see where you have applied it, and easier to tell if you have removed it all after the work is complete.

Masking fluid is great for creating negative visual effects, like you describe.