Standardize application of color css classes

Assuming colors are intended to help with us quickly compare different algorithms or data structures, it seems like the color styling--though subjective--should be applied consistently within each column.  For example, mergesort and quicksort both have a worst-case O(n) running time, so they should have the same color styling applied.  I have fixed several small inconsistencies like this.

I think it would be better overall if there were more css classes for each complexity class (something like progressively darker shades for constant, linear, log-linear, quadratic, etc) so that styling was less subjective, but you haven't made the stylesheet available in this repo.