Well, with blue tints in cosmetics like mascara and/or lash/brow colors, the objective is to create a complementary color for the eyes to make their natural color “pop” more readily. Blue is used to bring out the warmth and richness of brown eyes.
You see, on the color wheel, complementary colors are directly opposite each other. So color pairs such as red and green, yellow and violet, and blue and orange are complementary color pairs. When used together these colors cause one another to stand out more vividly.
Since brown isn’t usually found on the color wheel as a primary or secondary color we have to use the closest facsimile thereof, which is orange. (Brown is actually created by combining a primary and secondary color – red and green – which makes orange a component color – by the fact of the red and the yellow of the green color - and allows us to use Blue to bring out the orange tone of the brown color.) This doesn’t work with all shades of brown eye, since some are very dark, but it does make most brown eyes shine more brightly.

Answered by Ajay Chawla , an ibibo Master, at 1:51 PM on September 16, 2008