The size of the bubble is institutional wealth (larger is wealthier) and the color shows the spread between the percentage of students with no institutional aid (aka full-pay) and those with Pell. (Pell grants are awarded to students with the most financial need, usually coming from families that make less than $60,000 per year.) Red shows a dominance of full-pay, wealthier students, and green shows the opposite. This is interactive, so you can play with it if you'd like.
Comments and questions below, please. This shows about 1.200 Private, not-for-profit institutions. All Data is 2012 IPEDS, which is not adjudicated. Responsibility for accuracy lies with the institution.