It is good if reduce by 1px only to identify it as a quoted reply or make an Italicized font to see immediately but the people here are already used to the default quote so for sure most of them preferred this already, if this might be implemented its ideal if there's a feature of old and new so people would like to stick which they would like to prefer with.
I think the slight difference of the background color of quoted post to the actual reply is sufficient enough to notice that context is a quote. The main issue here is the readability of the quoted statement.
The improvement is good because it’s just a minor tweak on the font size and theymos can definitely change it quickly like the the additional (OP) tag for thread starter. This suggestion will be good if the improvement will have an option to adjust the size base on user preference because I don’t need to increase the text of the quote word if I’m the author of it since I know what I wrote.
