Watercolor is a medium known for its transparency and fluidity. There are three kinds of watercolor paint - tube, pan, and liquid.
Watercolor paint is admired for its transparency which represents the ability of light to pass through the paint and reflect the back of the white surface of the paper to create a glorious luminescent effect.
Transparency plays an important role when it comes to layering; it becomes essential to plan and layer the transparent colours to go above opaque colours, as they might not show up the other way around. You could make opaque colours more obvious by thinning them with water, but this will diminish their intensity.
So how to test which is transparent and which is opaque? In this book you will learn about it all.