Although I have a pre-association of this as a chihuahua's name (I know of one) so it colours it slightly for me. but I still think it's pretty neat. Not nearly as neat as Bowie or Spero mind you!
Darby does come across as rather yuppie-esque and popped-collar, compared to Bowie and Spero, which are edgier and a little more neon offbeat.
Darby is much more polite and makes me think of a salmon coloured shirt. I think I get the feeling that you are getting at with this name, though.. A kind of
Brit whimsy street-urchin spunk.
I like the word Spunkyboy.