Did you change the plug after you re-jetted or is that the original plug before your rejet?
The true and correct way to make 100% sure you're not too lean is install a new plug after a rejet. After the install, get it up to speed, ride for a couple of minutes, kill the bike. Pull the plug, then read.
If the plug was black before and now it's white could mean a number of things. You could have burned off excess carbon on the plug, or if you had a change in your climate while riding could affect the plug color too. Usually a white plug will indicate a lean mixture, but it's hard to say on an old plug.
As far as the next step, did you try removing the airbox lid to see if it still bogs at 1/4 throttle?
~Brian