MG Chemicals 4228 is the red varnish I use. It looks like
this when applied on a ballast. You can also use MG Chemicals 4226 if a clear/transparent product is desired. Both are rated to Class H and should be good for everything except 1000w ballasts, which use Class N varnish.
I get mine from a local electronics shop called
Sayal Electronics but here's some links to you folks in the US that might need to order it. A 55ml jar is enough for around 2-3 ballasts.
Digi-Key:
42284226Amazon US:
42284226eBay US:
42284226