In a transparent watercolor, the only white spaces will be those areas of the paper that remain unpainted. Consequently, white areas in this type of painting must be carefully planned for and protected against unintentional coloring. Opaque watercolors appear solid and cannot be readily seen through once they have dried. Gouache, casein, tempera, and acrylic pigments are all designed to remain opaque when applied straight from their containers. If these types of paints are mixed with water, though, they too can appear transparent or translucent.
Most watercolors are available from manufacturers in tube, pan, or liquid format.
All have their own attributes and drawbacks, but usually a specific type is chosen for a particular application. As mentioned above, other water-based paints such as gouache or acrylic can also be used as watercolor, again depending on the desired look. For the more initiated, watercolors can be made from scratch, but that route demands much more time, materials, and know-how. Years ago, watercolors were available mostly in a dry cake format, and this type of watercolor is still available today. These colors are typically partitioned in little tins, some of which contain a limited palette of colors that have a hinged top for storage.