Dogs are dichromats, which means they only have two types of cones in their eyes, compared to the three types of cones in human eyes. This means that dogs can't see the full spectrum of colors that we can, and they see the world in a more limited range of colors. Dogs can see shades of blue and green, as well as limited amounts of yellow and red. But, dogs are not able to distinguish between red and green.
As a result, dogs are not afraid of the color red. Dogs may be afraid of certain objects that are red, such as a red toy or a red ball, but this is not because they are afraid of the color red itself. Dogs may also be afraid of people wearing red clothing, but this is usually because the person is standing too close to the dog or moving too quickly.