Not sure what the marqueeWhite() method does, but the number seems to be an optional parameter.
example:
void setBrightness(int t=100){
// do something
}
if you now call setBrightness()
it would be the exact same call as if you would call setBrightness(100)
And should set the brightness to 100%.
The call setBrightness(30)
should set the Brightness to 30%
So what is actually happening with the number is defined in the method itself. If you see it in the source code, you will see what the default value is.