This is a good idea.
What colour would really stand out against the magenta paintwork so they can see the writing?
( Anthropos Was making beer on, Tue 26 May 2009, 9:00, archived)

Spunky white

(Bazongaloid, Tue 26 May 2009, 9:01, archived)

I believe on the Dulux paint chart it is known as
'Summer Jizz White'
( Anthropos Was making beer on, Tue 26 May 2009, 9:03, archived)

I believe it is available in a range
that stems from very very pale off white to a deep phlegmy green.
(Bazongaloid, Tue 26 May 2009, 9:04, archived)