While colored carrots are unusual, they're not exactly new. Purple and yellow carrots were eaten more than 1,000 years ago in Afghanistan and 700 years ago in western Europe. The orange ones are actually a recent cross between the groups in the past couple of hundred years.
The point is that yellow is a perfectly sensible colour for a carrot! This old traditional French variety has yellow roots with blunt ("obtuse") tips that are easy to dig up with no risk of snapping, and a good strong (but sweet) carrot taste.
Yellow carrots contain xanthophylls, pigments similar to beta carotene, which help develop healthy eyes and may prevent lung and other cancers. Lutein is a hydroxy-carotenoid constituting the macular pigment of the human retina. Increasing lutein intake from foods could increase the density of this pigment and decrease the risk of developing macular degeneration. Yellow carrots are a novel food source that could increase lutein consumption. Lutein from this novel food source significantly increases serum lutein concentrations and does not result in the decrease in Ŗ-carotene concentrations that accompanies administration of lutein supplements. (American Journal of Clinical Nutrition, Vol. 80, No. 1, 131-136, July 2004)