How do scientists know that certain animals are color blind?

Answer 1

When examining the eyes of the animal, they can see if there are rods and cones.

Rods allow for low-light and black/white vision. Cones are high-light sensitive and focus on a particular color. If there are no cones present, the animal is colorblind. If there is one or two types present, then there is a partial colorblindness that the animal is used to living with. Human have three types of cones (red, green, blue). There are other animals (such as certain species of fish and bird) which possess 4 or more types of cones, which enhances their visual color spectrum (even adding ultraviolet and infrared to their visual capacity).

Once the eye is examined, the scientist can determine the level of colorblindness that the animal has.

Answer 2

If the animal can be trained (ruling out clams and snails, for instance...) it can be thought ot look for food following a train of a given color, and avoid another color. If the animal would seek food randomly instead of homing to the location where the food really is according to the color code, it is because the animal cannot tell those two colors aprat.

Another way involves cutting the eye out and studying the compounds in the eye photoreceptor cells, find the colors that can be absorbed and those that do not get a reaction from the cell. It is a bit more messy, though.

Answer 3

I think you may be confusing being blind to colour (i.e. seeing in monochrome) such as dogs are with being colour blind-inability to differentiate between two colours.