Accessibility improvements

[mpilka]

Jeremy Stanley (fungi) pointed out:

• Colors aren't universal. in china for example, red means something is good
• Also red-green color blindness is fairly common, so labels can be important along with colors
• The bar charts which just list percentages and rely on colors to indicate a threshold is being hit can be an accessibility issue without some separate indicator as to what the threshold was
• For zuul's interface we also pair color coding with tooltips

So each color should be associated with label as well. This is already a case with Level 0 dashboard:

• Green associated with OK
• Orange associated with Warning
• Red associated with Critical

However it is not a case with e.g. percentage indicators. It may or may not be possible to achieve such labels together with percentage indicators with Grafana.