A poster colour is an opaque, water-based paint, similar in composition to watercolour but containing a higher concentration of pigment and an additive (like chalk) to ensure complete opacity and a matte finish.

Unlike transparent watercolours, poster colours are designed to deliver solid, flat fields of colour that fully cover the surface below, making them ideal for bold graphics, illustrations, school projects, and sign painting where maximum visibility and vibrancy are required. They are easy to use, dry quickly, and usually come in larger jars or bottles.