In the enduros I ride, orange is the predominant color, but there is a lot of other colors as well. I would say that either of your choices are fine, although I would expect you would have a much easier time finding a WR450f in your price range than a KTM.
If you are brand new to dirt bikes, however, I would recommend that you stick with the bike you have for a couple of years. Ride a few enduros with it. Don't even worry about timekeeping, just ride on the same minute with someone who does time keep and just follow him. When you get to the point where you can honestly say that the bike would have made a difference in your score, then it will be time to upgrade.
If you want to make that WR250 a bit more trail friendly consider adding a flywheel weight and adding a couple of teeth to the rear sprocket. Make sure your jetting is correct so you have decent power in the mid range. Work on your suspension.