why does rainbow have seven colors? why not less or more?

Because "color" is an interaction between the visible light portion of the electromagnetic spectrum and the light sensitive parts of our eyes.

Our eyes have evolved 4 different receptors--one each for Red, Green and Blue and another for violet.

A rainbow actually contains millions of colors, but we have evolved to categorize most of the wavelengths in the visible spectrum as one of the primary colors and their combinations.

If we had more types of receptors in our eyes, we would see more colors in the rainbow.

It does have more than seven colors, but the only colors that humans can see are ROYBGIV. Which stands for Red, Orange, Yellow, Blue, Green, Indigo, Violet. You can remember this by thinking of the multicolored clown named Roy B. Giv.

Infrared colors are below the wavelengths we can see, and ultraviolet colors have a wavelength above what we can see.

Bees see in a higher spectrum than humans so bees would be able to see more ultraviolet colors than you. to a bee rainbows have differnt colors.

A rainbow is just perfect, and that is how God made it.

here is a little rhyme to help you remember the seven colours.

Red, Orange, Yellow, Green, Blue, Indigo, Violet.

Richard Of York Gained Battles In Vain. .

Every colour of the rainbow means a lot more than 7 - unless you're buying a car I guess.

To see why rainbows are coloured at all check out the reference

A rainbow displays the entire visible spectrum. How many colors that is is a matter of arbitrary definition. In addition to red, orange, yellow, green, blue, indigo, and violet, there are all the in-between shades. We just don't attach special names to slightly more yellowish orange or greenish blue.

By Newton's Disc, it has been established that the sunlight consists fo only 7 colours. Rainbow is made out of the prism effect caused by the water droplets on the sun rays.

Because in your culture, you recognize seven colors. A rainbow displays all possible colors, so if your culture recognizes more or fewer, that's the number you will see.

The truth is rainbow has infinite number of colors, all within the color spectrum. But any language will fall short of names for each one of them.

Study wavelength theory, you will see that a rainbow is simply light diffraction into many many wavelengths. As many colours as you want depending on the bandwidth you want to assign to them.

We use seven as a convenient description only.

Rainbows have more colors but the ones you see are what humans can see, there are more colors in the heat spectrum that other insects or animals can see that we cant and vise versa.