Hate two-toned guns. Go with the Essex. Besides, all the other tricks on that one will make is a very comfortable piece. 
I cant agree more. Go with the Springfield.uglydog said:Since you allude to having a bit more than $500 to spend I personally would go for a Springfield Loaded. I am not overly familiar with Essex but what I recall being told is it is of middling quality frames and no one I know uses the slides. A decade or so ago I looked at an Essex frame for a semi-race build up but went with a Norinco instead. Around here Essex based guns (the few I've seen) have fallen between Rock Island Arms and Springfield Mil-Specs in price. Of the two you mention, it is a horse apiece. I would probably go with the Colt slide but would just as likely change my mind if I saw them.