Coloring macaroni noodles:

For intense colors, submerge noodles for 30 minutes or so in a solution of rubbing alcohol and food coloring.  Dry thoroughly on paper towels.  Here are some ratios for colors other than primary:

Orange: 2 drops red, 3 drops yellow
Turquoise: 1 drop green, 4 drops blue
Lime Green: 3 drops yellow, 1 drop green
Salmon: 3 drops red, 2 drops yellow
Violet: 2 drops red, 2 drops blue
Pistachio: 1 drop yellow, 4 drops green