Fix contrast ratios in site elements

[Inkering]

part of a series of accessibility improvements//maintenance taeyoon asked me to work on, I'm going to sort through and make PR's for these where possible

There are a few parts of the site which don't meet standards for contrast ratio, particularly the footer and some navigation elements. Namely, the grey color used and the teal//green highlight tone do not meet WCAG 2.0 standards for minimum or enhanced contrast. Hopefully we can change to a more contrasty highlight color.