None. Yellow is a "primary" color, along with red and blue. These three colors may be mixed together, two at a time, to produce orange, green, and purple...the "secondary" colors. All three, mixed together, produce brown.
When red and yellow are mixed they make orange. You can make red orange if you use mostly red, and yellow orange if you use mostly yellow. If the colors are mixed half and half you will have the secondary color shade of orange.
Brown. Purple is a mixture of red and blue. Orange is mixed red and yellow. Mixing red, blue and yellow together gives brown. You can alter the shade with different proportions, but it will be a shade of brown.
the primary colors (red, blue, and yellow) can be mixed to create the secondary colors (green, purple, and orange). blue + yellow = green. blue + red = purple. red + yellow = orange. if you mix the secondary colors (green, purple and orange) you'd get a muddy brown color.