Complete value from list with colons

[Scott Frazer <frazer.scott@xxxxxxxxx>]

I would like to do completion from a list of values that have ':' in 
them, something like:

_values foo a::b c::d

and have it offer 'a::b' and 'c::d' as choices, but I can't figure out 
how to escape the ':' in the completion system.

Thanks,
Scott