in reply to Re^2: How can I strip an arbitary number of "inner" spaces from a string?
in thread How can I strip an arbitary number of "inner" spaces from a string?

A bit shorter but should still work okay:
s/(\:)\s+/$1/
or just for fun:
s/(:) +/$1/
Second probably has loads of reasons why it'll fall over in other cases but seems to work fine here.