...to have the OP's posts and "my" (i.e., the user reading the thread) posts appear in different colours?
Currently they both appear on a background with exactly the same shade of green. Since the point of using a coloured background is presumably to make these posts stand out, could it be arranged that they stand out from each other?
This principle is already in place with MNHQ posts, which are blue. So why not make a user's own posts appear with, say, a pale yellow or pink background? To answer my own question from the thread title, it feels like it ought to take about 5 minutes tops to code this.