So I previously suggested a plugin to add custom highlights to inline metadata.
I figured out how, and decided to put it here instead of that thread as it probably is good enough to do the job without a plugin (and, as @ariehen points out here, with the new metadata model around the corner, all of this may be obsolete in a couple of months anyway).
span.inline-field-key[data-dv-key^="concept"] {
color: black !important;
background-color: green !important;
}
span.inline-field-key[data-dv-key^="session"] {
color: black !important;
background-color: orange !important;
}
Result:
