perl -le "$str='a\\:b:c'; my (undef,$x,$y)=split /((?:[^:\\]+|\\.)*):/s,$str,2; print for $x,$y"
a\:b
c

##</code><code>##

perl -le "$str='a\\:b:c'; my ($x,$y)=$str=~/^((?:[^:\\]+|\\.)*):(.*)$/s; print for $x,$y;"
a\:b
c