"De kleuren van de schoen zijn paars en roze."
Translation:The colors of the shoe are purple and pink.
"Violet is a "real" color that exists on the electromagnetic spectrum. It has a wavelength between 380nm and 450nm, sitting between blue and ultraviolet. When you split sunlight using a prism you will be able to see violet on one end. It is possible to describe violet in objective terms purely from a physical standpoint.
Purple on the other hand is a perceived color that is a mixture of red and blue. This effect is caused entirely by the human eyes and brain working together. The color purple doesn't really "exist" in that there is no wavelength of light we produce called purple. An interesting side effect of modern TVs and computer monitors that used RGB displays is that they cannot produce true violet, only purple."
Which is exactly why artists refer to violet as a shade of blue, because it exists in the blue part of the colour wheel.
I have had many arguments like this about the nature of colour, mainly because artists (such as i used to be) don't argue the facts of perceived colour because they believe it is self evident. An artist, unless they have a scientific education, will refer to the primary colours as red, blue and yellow, placing all other colours as a subset of those. A computer scientist will argue that it is red, blue and Green.
I know that both of these interpretations are wrong, that colours exist on a spectrum and are not definable by being a subset or mixture of other colours, but this interpretation is useful (and the way that it is the most useful to almost everyone), because it allows us to know how to mix colours to match.