Occasionally I'll open a question and find some of the text has been set to a lighter color than normal
instead of DARK:
I can't find anywhere that explains what this means.
Assuming that this refers to the colour of answer text, they are greyed out when their score is -3 or below to indicate that their content is not entirely reliable.
Such answers have been downvoted by a significant amount (scoring -3 or more), and have been made lighter to de-emphasize them.