Simple: You get violet (if the main colors are red, yellow, and blue – at least in pigmentary form).
However, if you’re talking about mixing these two additives (light) colors, it becomes magenta.
In addition to primary and secondary colors, we also have tertiary colors (they don’t teach you that in art class!)
In addition: red + yellow = orange; blue + yellow = green.
Imagine trying to create your own rainbow.
You have the well-known “fictitious” name: ROY G. BIV
Subsets of red:
Red, cherry, rose, jam, merlot, garnet, pink, vermilion, magenta, garnet, crimson, ruby, scarlet, wine, brick, apple, mahogany, blood, sangria, berry, currant, blush, candy, lipstick, raspberry, strawberry, maroon.
Subsets of orange:
Orange, tangerine, merigold, cider, rust, ginger, tiger, fire, bronze, gold, apricot, cantaloupe, clay, brown, honey, carrot, squash, spice, marmalade, amber, sandstone, yam, peach, sweet potato, tan, amber, chocolate.
Subsets of yellow:
Yellow, canary, gold, daffodil, flaxen, butter, lemon, mustard, corn, medallion, dandelion, fire, bumblebee, banana, sepia, butterscotch, dijon, blonde, pineapple, tuscan sun, lemonade, saffron, khaki.
(N.B.: Yellow, Orange, and Red are termed “warm colors”- red-orange, orange-yellow, violet-red)
Subsets of green:
Green, chartreuse, heather, evergreen, juniper, mint, sage, lime, fern, olive, emerald, pear, moss, shamrock, pine, parakeet, mint, seaweed, pickle, pistachio, basil, crocodile, avocado, thyme, oregano.
Subsets of blue:
Blue, slate, silver, slate, sky, navy, indigo, cobalt, teal, ocean, peacock, azure, cerulean, lapis lazuli, spruce, stone, aegean, mediterranean, blueberry, denim, admiral, sapphire, turquoise, arctic, jade, cyan.
Subsets of purple:
Purple, scarlet, mauve, violet, lily, boysenberry, lavender, plum, magenta, lilac, grape, periwinkle, sangria, eggplant, jam, iris, heather, amethyst, raisin, orchid, mulberry, wine.
(N.B. Green, Blue/Indigo, and Purple/Violet are termed “cool colors”- yellow-green, green-blue, blue-violet)