I was recently informed by Now Support that UI styles cannot be applied to read-only fields, and for this 7-year-old known issue, PRB663205, "after carefully considering the severity and frequency of the issue, as well as the cost and risk of attempting a fix, a decision has been made not to address this issue in any current or future releases."
I'm posting this here to see if there's is indeed demand from the community at large for this feature to work properly. To me, it doesn't make sense that I cannot modify the appearance of a field simply because I can't edit the value in the field.
