FIX: WCAG-AA compliant topic list heatmap colors (PR #9380)

Color #ec7213: 3.0, Bold - AA Large Pass Color #b06318: 4.50, Normal - AA Pass Color #93704a: 4.51, Normal - AA Pass

Used the Chrome Inspector color picker curves to preserve the hue and make minimally invasive changes to the coloring.

Screenshot of Meta with the new styles applied. I can hardly tell the difference ^.^