If you're getting that color and it's 4 stroking at WOT, then you need to increase the size of your main jet. The reason it's half and half is that the tip is the hottest part of the plug, and since you're not lean all through the range, it only toasts the tip when you're wide open.
A new perf filter will help as you are allowing more air into the engine. If it 4 strokes, means there are too much full for the same ammount of air. Maybe will you need to re-jet your main jet, to a lower number, try 0.65mm
To clean the filter all you have to do is wash it in warm soapy water. Wring out the water install it and go ride it. You won't need to oil the filter it will self oil.
This is for a foam filter don't wash a paper one.
If your engine is 4 stroking wide open then you need to lean out the main jet go one size smaller. You may also need to readjust the needle once you do put in a smaller dia. main jet.
Here's something to think about and try. Before you go and buy a new carb . You will still need to learn how to tune the new carb too. So give this a read and try.
If your 4 stroking a wot and running lean at less throttle setting. Sounds like your needle is set way to lean, along with the main jet too big. You are probably trying to get rid of the 4 stroking at wot by changing the wrong thing, aka the needle. Changing the main jet one size smaller will help this condition, but you will also need to richen up the needle along with the smaller main jet. if your running a 0.70mm main jet go to a 0.65mm main jet set your needle on the #2 slot give that a try. you may have to play with the needle some by going up or down a notch from the normal #2 slot, if it's one of those sorry shaped ones, some needles are not tapered properly then you will have a little more problem adjusting it, it can be done .One way involves spin sanding with 2000 grit wed/dry sand paper, and you will only want to remove a 0.001 or 0.002. You will need to mic the needle from the fat end to the small end first . Then let me know I'll give you a set of numbers to shoot for if you decide to try that but doing this would be only if your needle is way to fat to start with.. Running with out the air cleaner will ruin the engine, especially if you happen to get a rock sucked into the air intake or if you ride in a dusty area or dirt roads. Ever notice how dirty the engine will look around the carb and top of the back side of the engine? That's the dirt and trash off of the road kicked up by your rear tire. Paved roads are not much cleaner than dirt roads so running very long with out a filter is going to hurt your engine.
Good luck guys.