Off the top o' my head, I'd say add an extra field to the "thread" table called "threadcolor" and make a plugin that will wrap tags around the title if the colour field is set. But then you have to enter a colour for each thread....
Unless I'm reading that wrong and you just want to colour all threads made by you as a different colour. That'll be easy.
Open up your AdminCP, go to Plugins & Products, click "Add New Plugin". Product you can leave a vBulletin (unless you wanna make a new Product for this, but you can do that at any time, really).
The Hook Location you should select is "threadbit". Title it "Coloured Titles fer me! Yay!" Leave the Execution order at default (5). Enter this code for the plugin itself
PHP Code:
if ($thread['postuserid'] == INSERTYOURUSERID) {$thread['threadtitle'] = '<span style="color: INSERTCOLORCODEHERE;">' . $thread['threadtitle'] . '</span>';}
Set it to "Yes" to turn it on, test it out, and bada bing bada boom, coloured title, yay! :3
--------------- Added [DATE]1246273228[/DATE] at [TIME]1246273228[/TIME] ---------------
Oh, note, replace INSERTYOURUSERID and INSERTCOLORCODEHERE, of course.