As I'm fishing very often in dark environment it's difficult to visualize the loading point, therefore I would like to paint some black marking using permanent marker pens.
Is it safe for the Fly Line coating to implement permanent marker pens ?
May I offer another alternative?
A fishing company called Gardner offer a glow in the dark line marker paint that you paint onto the line. With a short charge from a UV or normal torch, you get about 4 hours glow.
It is semi permanent and flexible, so you can remove it with your nail if you want to.
It is specifically designed for line (mono and fluorocarbon), so it does not contain any solvents etc which will damage the lines surface, and it goes on a flyline nicely. Just use 3-4 thin coats and build a nice layer.
The 2G plus glows more than the 2G.
My suggestion would be to mark the line just above where you would hold the line on a cast, so you can see it just above your hand, making it nice and easy to gauge where the head of the line is.
I have used this on shooting heads and marked the join, but really, having it closer to your upper hand on a spey line would make much more sense to me.
http://gardnertackle.co.uk/product/glo-pro-2g/