use Data::Rmap;

@days=qw(mon tues wed thurs fri sat sun);
@cols=qw(red orange yellow green blue indigo violet);
@vars = (\@days, \@cols);

rmap {s/e/E/g} @vars;

print Dumper(\@vars);
--
$VAR1 = [ 
          [
            'mon',
            'tuEs',
            'wEd',
            'thurs',
            'fri',
            'sat',
            'sun'
          ],
          [
            'rEd',
            'orangE',
            'yEllow',
            'grEEn',
            'bluE',
            'indigo',
            'violEt'
          ]
        ];