Checkmarks next to all correct answers

Can you tell us a bit more about this:

"We are finding challenges with color alone being an indicator."

As an example, a MC question with 4 options and A and D are correct. User selects A and B and hits Submit. The question then shows a gren check mark to the right of A (because the learner chose correctly) and a red X beside B (because the learner chose incorrectly. The check box area for each option also uses color coding - A and D are shaded light green to indicate they are correct responses, B is shaded in ight red to indicate it was an incorrect option.

Is it that your learners aren't recognizing what the shading is trying to communicate?

Is it that your learners aren't recognizing what the shading is trying to communicate? <-- yes this is precisely it. Some have noted that it is not accessible for red/green color blindness and other potential issues. Are you suggesting we correct this by making a light shade the correct indicator? We can examine our theme again, as I think our colors have gotten a bit saturated (the particular one I'm looking at is blue, red and green - all the same shade/tone).

The main argument I'm hearing for the check mark is that it is more easily/commonly recognizable as an indicator for "correct" than a lighter shade.

Added: we have had a recent past experience with an accessibility engineer that has required us to put checkmarks on other items (not dominKnow content) - for similar reasons. So it might be boiling down to an internal requirement where the tone differentiator isn't enough (I appreciate your time in exploring this with me ).

https://webaim.org/articles/contrast/#sc141 - see section 1.4.1: Use of Color:

Color is not used as the only visual means of conveying information, indicating an action, prompting a response, or distinguishing a visual element.