Question about subtractive color mixing
The pink color of the mixed red and white is an optical illusion, similar to how inkjet printers create all the colors from inks of three primary colors by printing combinations of tiny colored dots close together.  

The color in paint is particles of finely-ground pigments (colored powder), suspended in a liquid that dries into a film.  When you mix red and white paint, you get a suspension of red particles and white particles.  There is a mix of those particles on the surface of the paint.  

The red particles reflect just the red light.  The white particles reflect all the colors.  The individual particles are too small to differentiate with the naked eye.  What you see is a blend of the light reflected by the different particles on the surface.