Product review (4 stars): I can usually see the yellow paint fairly easily. When I first shook the pen the cap ...
I use this when repairing my car engine to place marks on the parts before I remove them.  That way I can line up the parts properly when I put everything back together.  I can usually see the yellow paint fairly easily.  When I first shook the pen the cap and nub came off.  But the pen worked OK after I reinserted the nub.  The pen is cheap enough that even if it only lasts one or two jobs I will be satisfied.