Magenta is a colour which is hard to make, some people even say its primary colour, the most people use warm red like scarlet or vermillion and mix with a warm blue or violetit will end up with a muddier colour like maroon, this is the main problem, but i mixed crimson red and a cool shade of purple and it made a vivid magenta that i wished,. And it is a shade of cool pink which is a purplish red colour. The colour shown in this video is not actually a real magenta hence it looks like a shade of red like geranium
Usually in any color mixing class, the instructor will warns you to never use black to any colors because the color will loose its vibrancy and will look deadened . And white added will turn the mixture into gray.