I have a bike that does the same thing, and I do know how to fix it but I'm to lazy to do it. So, heres the problem, your too rich on the needle and maybe pilot as well and to get it to idle you turn in the idle screw, to get it to idle creating a larger opening between the slide and body. As we all no colder temps create a leaner condition so when you start it it is a bit on the leaner side and your putting more air in causing more revs, once warmer you get back to the richer condition and it idles fine. Other than your bike running a bit rich, and you don't let it rev to the moon using the kill switch to keep it from revving to high you really don't have a huge problem. Most Kawasakis are jetted to rich from the factory, especially the needle, it is not un common to drop 3-4 needle sizes on a 250 as well as main and pilot. Jetting is an art and does take time to get right, what works for me won't necessarily work for someone else, remember temperature and humidity play a big part in jetting. At the race track it is amazing how many bikes you see that aren't jetted properly, 250's are the most common because they run well even if jetted wrong, 125's on the other hand have to be jetted right to be competitive on a pro level.
so there you have my .02 on the issue.