Related is that English has 11 basic color terms: black, white, red, green, yellow, blue, brown, orange, pink, purple, and gray. As a result, trying to teach cyan and magenta as primary colors will be much harder than teaching blue and red as primary colors.

For more on basic color terms: https://en.wikipedia.org/wiki/Color_term#Basic_color_terms

You don't think 5-year-olds can learn two new fancy colors?

While you are right, "magenta" is just a fancy synonym for "purple". It might have been chosen instead of "purple" because the traditional word could be applied to colors having various proportions of red and blue, while "magenta" is intended to convey that the amounts of red and blue are equal. However all the traditional color names, like "red", "green" or "blue" refer to wide ranges of hues, not to a precise hue, so there was really no good reason for the use of the word "magenta".

"Cyan" is a very bad word choice caused by confusions in the translations of Ancient Greek texts made by philologists ignorant of chemistry and mineralogy. In Ancient Greek, "cyan" meant pure blue, not blue-green. More precisely, it was the color of the ultramarine blue pigment, the most expensive blue pigment at that time, which was imported from the present territory of Afghanistan and for which the name "ku-wa-no" was already used by the Hittites, a millennium before the Greeks. Nowadays ultramarine blue is still used as a pigment, but it is made synthetically, so its cost is a small fraction of what it was before the 19th century.

Before the use of "cyan" has started, the color name "blue-green" had been used for a very long time. Similarly, "orange" is a relatively new English word, but the color had been mentioned for many centuries, as "red-yellow" or "yellow-red".

So the awareness of distinct hues is not necessarily limited to the set of simple color words, because most languages have used compound words to name the hues for which they did not have a simple word.

Other languages have used the names of well-known colored objects to distinguish the hues that did not have distinct names. For instance, in Latin the word for "red" was used for both red colors and purple colors. When Latin speakers wanted to specify whether something was red or purple, they would say "red like the kermes (red) dye" or "red like the purple dye" (the word "purple" as a color name comes from the latter expression). Similarly, in Latin the word for green meant either green or blue-green. To distinguish the 2 colors, a Latin speaker would say "green like grass" or "green like leaves" or "green like emeralds" for expressing "green" and "green like the littoral sea" or "green like beryls" or "green like turquoise gems" for expressing "blue-green". So they were well aware about the differences between these colors, even if they did not have distinct words for them.

Eliminating from your 11-item list the words that cannot designate saturated colors, i.e. black, white, brown, pink and gray, there remain 6 words for saturated colors: red, orange, yellow, green, blue and purple.

Besides these 6 words, 2 more words are useful for naming saturated colors. The use of the word "violet" is widespread enough that it should be added to the list as a basic English color term.

The distinction between violet and purple is that while both are mixtures of red and blue, violet contains a small enough amount of red that it can be matched by a monochromatic color in the violet range of the spectrum, while purple contains an amount of red that is great enough so that it can be matched only by a mixture of monochromatic red with monochromatic blue.

A word is needed for the blue-green color. Cyan is a misnomer that should be avoided, but "turquoise" is a word that has been used in English for many centuries for designating the blue-green color (and which is used for the same purpose in many other European languages, all of which have borrowed the word from French, like also English). "Teal" is another synonym for "blue-green", which has been introduced in the 20th century.

There have been many misunderstandings about the words used by Isaac Newton for his circle of colors, but I believe that when his words are interpreted correctly, he was right.

Isaac Newton has divided the saturated colors into 8 colors: red, orange, yellow, green, blew or blue, indico or indigo, violet and purple. The first 7 of these were classified as prismatic colors, i.e. as monochromatic colors.

Isaac Newton spelled blue as both "blew" and "blue", and also indigo was spelled as both "indico" and "indigo". While the meaning of the other color words is not ambiguous, the meaning of these 2 words is not clear.

The words used by Isaac Newton were the names of some paints, whose hue he compared with the colors obtained by the dispersion of the solar light. The "indico" paint was presumably made with the indigo pigment, so it must have been blue.

The "blew" or "blue" of Isaac Newton was the color of the "blue Bise" paint. "Bise" is more frequently spelled "bice" and it was the name of a paint based on copper carbonate. Depending on the exact details of its method of preparation, such a paint will contain a mixture of malachite and azurite pigments, so it might have any hue between green and blue. We do not know who was Newton's paint supplier or any other details about the paint used by Newton, so it cannot be known for sure which was the real color of Newton's "blew".

Nevertheless I assume that Newton's "blue Bise" was actually a blue-green paint, because only in this case Newton's classification of the saturated colors will make perfect sense, because blue-green and blue are distinctive enough to deserve to have their own names.

So translated into modern English, the 8 saturated colors of Isaac Newton would be: red, orange, yellow, green, turquoise, blue, violet and purple. This classification remains right.