The basic colour wheel of Itten is good in principle

BUT

when it comes to Primary colours it is more accurate to have a red that is magenta (ie crimson or Red-blue shade), a blue that is cyan (ie turquoise or blue-green shade) and yellow (ie lemon yellow or yellow-green shade).

(In Itten's system you get very muddy purples.)

Of course when mixing colours experience becomes as important as theory, but theory helps the learning painter to get started.

Surely in theory you get a grey often very dark but not black.

Optical greys (as opposed to black plus white) are obtained this way and are often very beautiful.

The pigments cerulean blue (Cölinblau) and light red (Lichter Ocker gebrannt) make a lovely grey (with the addition of white).