While you can technically use white paint as a substitute for primer, it's not recommended. Primer is specifically designed to create a surface that paint can adhere to while also sealing the surface and blocking stains. Alternatively, paint is designed to add color. So while white paint can provide a base coat, it will not offer the same adhesion and stain-blocking properties as a primer. In most cases, it's best to use a dedicated primer before applying paint for a more professional and durable finish.