If you mix turquise and purple you get blue. However, making red and blue is generally quite hard to do with additive color mix (RGB). In printers you get red by mixing yellow ang magenta dye. You get blue by mixing cyan and magenta because this is subtractive color mixing. In color print you have three colors plus black. read more
"Secondary" colors are made by combining two primary colors. Since you need to combine red and yellow to make orange, orange is considered a secondary color. The other two secondary colors are violet and green. read more