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]

Excellent job! It works perfectly!
Thank you very much!

This method will allow records to appear in any order, meaning that "Peter white" and "Peter brown" don't necessarily have to appear grouped together in the original data set. That's the pro to the following solution. The con is that there is no effort made to preserve the original order (just as no assumptions are made that the original set came in any particular order in the first place). It would be trivial to sort alphabetically though, or even to keep track of original order if necessary.

A hash of arrays is used, and color values are pushed into arrays keyed off of the name field. Here's the code:

use strict;
use warnings;


my %sets;

while( <DATA> ) {
    chomp;
    next unless length;
    my( $entry, $color ) = split /\s+/;
    push @{$sets{$entry}}, $color;
}


foreach my $entry ( keys %sets ) {
    print $entry;
    foreach my $color ( @{$sets{$entry}} ) {
        print "\t$color\n";
    }
}


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

#!/usr/bin/perl -w
use strict;

my %hash;
(!/^$/) && (push @{$hash{(split /\s+/,$_)[0]}}, (split /\s+/,$_)[1]) w
+hile(<DATA>);

for my $key (keys %hash) {
    (print "$key\t$_\n" ) && ($key="") for (@{$hash{$key}}) ;
}
__DATA__
John     red
Mike     yellow
Peter    white
Peter    brown
Jim      purple
Antony   orange
Antony   green
George   black
[download]