This was done with wood arrows but it's the same for all materials.
first I tape off with masking tape what I didn't want white. Then I simply spray and let dry.
Once it was dry, I wanted the back section to be blue to match the feather splice, so I taped off the white end cap that I wantted to stay white and spray painted blue.
be sure that when you apply your masking tape that the line of the tape is perpendicular to the shaft.
After I remove the masking tape they look like..
then I crest
and the finished arrow.
There are a few detail steps I left out but this is general idea of how I use masking tape and spray paint.
Derek