The color ball denotes page level in the site structure:
= 1st level page, accessible directly from the NYCHS home page.
= 2nd level page, accessible from a 1st level page.
= 3rd level page, accessible from a 2nd level page.
= 4th level page, accessible from a 3rd level page.
= 5th level page, accessible from a 4th level page.