Ember Quiz Stats - a11y/color contrast

Closes CNVS-13078

TEST PLAN
---- ----

  - visit ember quiz stats
  - verify the colors are updated as requested in the jira ticket
  - verify that when you hover over a bar in the bar charts you no
    longer see the bars turn to the orange-red color

Change-Id: Ia0e6380dc1ee4ab5971edd4628d9ec75844a5b64
Reviewed-on: https://gerrit.instructure.com/36070
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Jason Madsen <jmadsen@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Product-Review: Ahmad Amireh <ahmad@instructure.com>