When a course module is visible to the user but hidden from students, it has the .item-dimmed class applies.  I tested the contrast of the text on the background colour against WCAG using Colour Contrast Analyser, and it failed:

Foreground:#818181

Background:#F8F8F8

The contrast ratio is: 3.7:1

Text failed at Level AA

Text failed at Level AAA

Large text passed at Level AA

Large text failed at Level AAA

.item-dimmed currently sets opacity to 0.6. Raising this to 0.7 passes AA, and 0.85 passes AAA.