Figured this one out, but needed SSH access so I could do a "grep -r lightblue" through the templates. :-) The
styles/subsilver2/template/ucp_pm_history.html file seems to have the code in it.
Code:
<td width="100%"<!-- IF history_row.S_CURRENT_MSG --> style="background-color:lightblue"<!-- ENDIF -->>
How nice that they just "assume" lightblue. All this themeing and CSS support yet no use of classes there... Silly silly silly.
Anyway, I've changed it to
background-color:#3355aa; which is the same thing we use for the "tt" block here in posts. It looks good to me; screenshot attached.
I can make it a little darker if some people find the grey-on-blue text too hard to read -- let me know!
EDIT: Actually, to make it more consistent with the UI, I think it should use the same colour as the "Attachments:" bar background colour here in posts. That seems to be readable. But I'd like feedback from folks first.