In that case bubble sort and insertion sort should be green for the best-case time complexity ( O(n) vs. O(n log(n)) for quicksort/mergesort).
It might also be interesting to make the plot dynamic and allow the visitor to play with different implicit constants for the individual asymptotic bounds.
O(log n) green
O(n log n) yellow
Which is weird, since green-green-red-yellow-red is a really confusing order. I don't know why they did it that way.