Hi, This will help you only if duplicate lines are collectively.

use strict;
use warnings;

my $pre = '';

while (<DATA>)
{
    chomp($_);
    next if /^$/;
    my ($name, $color) = split /\s+/, $_;
    ($name ne $pre) ? (print "$name\t$color\n") : (print "\t$color\n")
+;    
    $pre = $name;    
}
__DATA__
John     red
Mike     yellow
Peter    white
Peter    brown
Jim      purple
Antony   orange
Antony   green
George   black

Output:
-------
John    red
Mike    yellow
Peter   white
        brown
Jim     purple
Antony  orange
        green
George  black
[download]

Updated : TIMTOWTDI
If duplicate lines are not in collective then use this,

use strict;
use warnings;
use Tie::IxHash;

my %hash;
tie %hash, "Tie::IxHash";
while (<DATA>)
{
    chomp($_);
    next if /^$/;
    my ($name, $color) = split /\s+/, $_;
    ($hash{$name}) ? ($hash{$name}.="\n\t$color") : ($hash{$name}="$co
+lor");        
}
print "$_\t$hash{$_}\n" for keys (%hash);
__DATA__
John     red
Mike     yellow
Peter    white
Jim      purple
Peter    brown
Antony   orange
George   black
Antony   green

Output:
-------
John    red
Mike    yellow
Peter   white
        brown
Jim     purple
Antony  orange
        green
George  black
[download]