Color theory in the Renaissance had much to do with individuality and clean-ness of lines. According to one critic, artists who created masks for balls in the Renaissance:
"began to explore new approaches...merely by achieving more and more realism. They evolved an amazing knowledge of perspective, light and shadow, correct proportions, and they used colors with an increasing artistic freedom. Still, the procedure was largely a matter of preparing a perfect outline drawing, and coloring each section in the neatest possible manner.
The High Renaissance, around the turn of the sixteenth century, was the culmination of all these efforts. Individuality in art was at last established. Composition, color, the entire concept of a painting, were more and more individualized. You could see the mentality and temperament of the artist, as well as his talent and his skill, in his paintings."
Applying this knowledge in recreating a mask like one worn in Romeo and Juliet, you would want to take the this realism and the personality of the characters into consideration. How, for example, would a love-sick Romeo's mask differ from the no-nonsense mask of his friend Mercutio?
For examples of a selection of Renaissance masks, go to Google images and type in "Renaissance Masks."