Thanks Walter, very valid point.
Sorry Ken,
Just realised not all your questions was answered..
I use Acrylic paints, usually the artist type paints that you can mix together and get the colour you want or just use a standard colour. You can usually get them quite cheap from the likes of B&M or the likes of pound land" Aldi did a selection a short while ago that was quite good.
I usually paint the inside of the blanks and the tubes the day before gluing up, give the paint time to dry. After drilling the blank I will also check to see how loose the tube is, if it's a little too snug I have drilled it out a little larger just to enable the paint coat thickness to avoid damaging the paint on the way in.
If you use Epoxy glue you can mix a very small amount of colour to the glue as well just in case you scratch the reverse paint off in the way in.
Some turners use car paint acrylics and spray them, they work well but I don't like the smell or the conditions it creates so keep away from them. Nail varnish is also good, but be careful with that one as her in doors might have something to say about that.
Permanent marker pens are another good one that has been used with good results.
Whatever you use and try, remember if it doesn't work then you may as well not bothered and wasted your time doing it as it will end up in the bin. So once you find a way it works stick to it, that is what everyone on here will do.
They all have their own preference. Look forward to seeing which ones you try and let us know what success you have.