The pipe will go gold first, then blue, then blue black.  It means hot, hotter, hotter.  Running lean or rich can cause it.
If this is new to your bike it may be environmental.

In general...

thinner air = go leaner (Barometric pressure decrease)

hotter  air = go leaner
more humidity = go leaner
higher altidude = go leaner

thicker air = go richer (Barometric pressure increase)

cooler air = go richer
less humid = go richer
lower altitude = go richer


Barometric pressure effects jetting in a big way, humidity, air temp, and elevation.  Some places have extreme  variations in barometric pressures and if you live there, your pipe will blue.  I live in the high desert and temps can change 40 degrees f in a couple hours, humidity can vary wildly too.  No way to jet for that.  

Gold and blue are pretty!

You should go ahead with the spacer & air screw adjustments to get rid of that irritating backfire!

I had trouble with the carb top screws also, a fat screwdriver and needlenose vise grips got them no problem.  You should be able to clamp down hard enough on the stripped one & one's you can't reach well to be able to remove them without  using a screwdriver.

And of course replace the screws with hex ones when you're done.

-Brad