They exist indeed.
I have different colors like white,gold,silver,whiteblue etc.
The pen has an liquid-ink inside and are supplied through a very thin tube
(aprox. 0.3mm) with a thin rod sticking out about 0.5mm at the tip which
lift the valve inside.
They write very clean/nice and permanent.
I bought them in Germany on my holiday.

"N Cook" skrev i melding
...
For permanent marking missing legends or other added comments to black
cased
ICs.
Do they exist?, not necessarily Staedler or even white , just something
thats not dark red,green,black or blue, that stays on and contrasts with
black plastic.

--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://home.graffiti.net/diverse:graffiti.net/