I managed to get this, stemming somewhat off of yours and hitting up regex and using the hook location postbit_display_complete.
PHP Code:
$pattern = htmlspecialchars('/>.*/');
$replacement = '<span style="color:green">text</span>';
$this->post['message'] = preg_replace($pattern, $replacement, $this->post['message']);
This replaces anything after > on one line with the green word "text".
It seems I can perfectly call the text, but I cannot change its color. If I try to input "<span style=\"color:green\">$pattern</span>"; or any such thing in, it simply returns />.*/ instead of the actual text that regex defines. This occurs even when I place the regex itself in the span tags.