It's simple supply and demand. If a minority of the engineers graduating from college have a particular trait (e.g. blue eyes), then if Silicon Valley companies

It's simple supply and demand. If a minority of the engineers graduating from college have a particular trait (e.g. blue eyes), then if Silicon Valley companies compete to have a 50/50 split of blue eyed engineers vs non-blue eyed engineers, they'll end up paying blue eyed engineers more for the same skill level. (Unless the skill distribution of blue eyed engineers is somehow skewed higher than non-blue eyed engineers.)