When we see an object lit by white light, its color is due to the object absorbing some colours and reflecting (or transmitting) others. For example, green foliage appears to be green because it contains pigments that absorb blue and red light and reflect only green light. It is a similar story when the light is viewed through an object, such as a photographic filter. You only see the part of the spectrum that is allowed through. For example, a blue filter blocks red and green light, and allows only the blue part of the spectrum through.

Photo by Caley Taylor

By Chris Rutter, “Color Theory Fundaementals for Digital Photography”