Is it possible to define or explain colors?

No, it is not possible to explain colors or any other perceptions like sound or taste. Colors are interesting, because, you would think that since colors have a continuous range of frequencies then that would be how we perceive them, but that is not the case. If fact, we can see colors that are outside the spectrum of the rainbow. We have red, green and blue color neurons, and what we perceive are combinations of reds, greens and blues. You can see this for yourself if you go to a color choice on your computer and select different combinations of red, green and blue.

I think I could. Not that I’m completely disagreeing with @LostInParadise . The complex colors would be a bear to explain. With some really abstract thinking and a lot of work I could convey the basic colors and work from that. It would take a lot of use of sensation and textures but I think the concepts could be described. I gave a blind person a ride home from the fireworks on a 4th of July and we ran into someone he knew. He described the fireworks as beautiful even though he had no sight at all. It inspired me a lot.
And welcome to fluther.

Light exists over a range of electromagnetic frequencies carried by photons. Many creatures have a visual sense that can detect some of them. Insects, for example, can perceive infrared frequencies that are below the range that human eyes can detect. Other creatures can perceive ultraviolet frequencies that are above this range. Our eyes have six kinds of receptors in our eyes called cones existing in complementary pairs that can detect “visual” light.

When we communicate about our sensory experience, we use analogy. All our words can do is compare one experience to another and point out similarities and contrasts.

When we learn to name our colors as children, we have to begin with the actual experience of color: Mom shows you Red—gives you the experience—and tells you that this experience is called “red”. You now have an experiential benchmark against which your further experience of color can be measured. You then have to learn that the label “red” is flexible enough to encompass a wide and subtly variable range of experience, similar to but different from that original benchmark experience.

So all of our communication about experience has to start with experience itself. Words aren’t capable of creating the experience; they can only refer you back to your stored experiences and synthesize new imagery using analogy.

You can describe colour scientifically by talking about wavelengths in the electromagnetic spectrum but as @thorninmud says to describe the experience of colour to someone who is blind would be impossible.

Sorry, @flutherother, but the word ‘blind’ does not appear in the question. I agree that explaining color to someone who has never experienced vision would be difficult if not impossible. One might try to make an analogy with another sense, like smell, taste, hearing or touch, but none of these can truly replicate the experience of vision.

This distant relative of my hubby tried

Somethings cannot be put into words,it can only be experienced. Color is one such thing.

Colors can be defined- otherwise you would be looking at a monochrome screen. You can define anything, whether it exists or doesn’t. Definition is a primitive logical process, and is meaning-free on its own.

Colors can be explained, but the explanation may be unsatisfactory and may need to be refactored for each person. There may be at least one explanation which is satisfactory for any given person, but I am sure that’s not provable.