There are only two types of fabrics for marine canvas covers: acrylic and coated covers. The main differences between the two types are the chemical construction and the manner in which they are made.
Acrylic are also known as solution-dyed acrylics, which means that the solution from which the fibers are made are the color that the canvas is going to be eventually, so there's no fading or discoloring from sunlight and other elements. In most other cloths, such as with clothing, the fiber is colorless and then dyed the chosen colors after the fibers are woven. The fibers from a blue acrylic boat cover, for example, are woven from a solution that is liquid blue before it is spun into fiber.
Coated material for covers are commonly different types of vinyl coated polyester. The color of the cover is usually the color of the top vinyl layer, and the underside usually shows the natural color of the polyester that makes up the other layer of the fabric. The physical qualities are also very different from acrylic fabric covers, which can breathe because of the manner in which they are woven. This should be taken in to consideration depending on what the fabric is used for. Coated material fabrics need vents to allow air to circulate if that is required.