ok, I worked out an easy way to do that
create a directory on your theme called ‘bbpress’
ie wp-content/themes/%your-theme-name%/bbpress
where %your-theme-name% is the name of your theme
find
wp-content/plugins/bbpress/templates/default/bbpress/loop-single-reply.php
Make a copy of this file, and put in in the directory called bbpress that you created above, so you end up with
wp-content/themes/%your-theme-name%/bbpress/loop-single-reply.php
bbPress will now use this template instead of the original
and you can amend this
so replace line 61 which reads
<div class="bbp-reply-content">
with
<?php
//now check if it is the topic author
$author = bbp_get_reply_author_id(bbp_get_reply_id()) ;
$current_user = get_current_user_id() ;
if ($author == $current_user) {
echo '<div class="bbp-reply-content bbp-author">' ;
}
else echo '<div class="bbp-reply-content">' ;
?>
then just add the bbp-author css styling to your theme’s custom css
eg
.bbp-author {
background : green ;
}
you might require
.bbp-author {
background : green !important;
}
depending on where you put the css.