Responding, no doubt, to Wittgenstein's famous dictum that there is no transparent white, Binney and Smith, the producers of Liquitex, have made an acrylic transparent white. It seems to be a white with so little opaque matter in the tube that the acrylic medium is acting as the transparent matter. The refractive indexes of pigments are very close to the index of the paint vehicle. They are used to provide bulk, control setting and contribute to the hardness, durability, and abrasion resistance of the paint film. Because they are commonly used to add bulk to other pigments, they are called extenders.
Most transparent pigments are natural minerals reduced to pigment particle size.
Transparent pigments often constitute a substantial portion of a protective coating. These pigments are essentially transparent to visible light. Because of the difference in refractive index between the pigment particles and the vehicles, white pigments refract the light from a multitude of surfaces and return a substantial portion in the direction of illumination without significant change in its spectral composition. W. Karl Watson , Painter Color can be transparent. Watercolors are transparent.