You won't get a perfect black by mixing paints. You might manage something close by mixing blue and red and then adding a little yellow.
If the result is too green - add red.
If the result is too brown - add blue.
If the result is too purple - add yellow.
You will get best results if the blue is a turquoise blue (cyan=C), The red is slightly purplish (magenta =M) and the yellow is yellow (=Y). The colour printing process used for books magazines and newspapers uses these three colours to get all the colours visible on the page, but because a true black cannot be made, an extra ink (black =K) is also used. You will find the same CMYK combinations in ink-jet printers and colour laser printers