To meet the AAA standards of the WCAG accessibility guidelines text and backgound colours should have a minimum contrast ratio of 7:1.
Useful tools:
Contrast combination rules for grid format
F must have strong contrast against E
H must have strong contrast against G
B must have strong contrast against A
A should have strong contrast against Moodle page background (currently #fff)
Suggestions
Make E and D the same colour.
Make B, C and I the same colour.
Set defaults for G and H across whole school (Eg #222222 on #EEEEEE)
If using ‘outside’ option, C must be thin enough to allow B to be clearly legible (not greater than 2px)
If E or F has good contrast against #fff, use it as A with the other as the B (either repeating the main colour scheme or inverting it).
Colour ideas
#657697 - Ducksoup