One way

#!/usr/bin/perl --
## 
## 2014-06-09-12:49:11
## 
## 
## perltidy -olq  -csc -csci=10 -cscl="sub : BEGIN END if " -otr -opr 
+-ce -nibc -i=4 -pt=0   "-nsak=*"
#!/usr/bin/perl --
use strict; use warnings;
use Tk;
use Tk::Table;

Main( @ARGV );
exit( 0 );

sub Santeria {
    my( $w ) = @_;
#~     my( $w , $table ) = @_;
    my $table = $w->parent;
    $_->configure( -background => 'white' ) for $table->children;
    my( $row, $col ) = $table->Posn( $w );
    print "row=$row, col=$col\n";
    $w->configure( -background => 'grey' );
} ## end sub Santeria

sub Main {
    my $mw    = MainWindow->new;
    my $table = $mw->Table->pack;
    for my $iy ( 0 .. 5 ){
        for my $ix ( 0 .. 5 ) {
            $table->put( $ix, $iy, "x($ix),y($iy)" );

        }
    }
    
#~     $table->bind( 'Tk::Label', '<1>', [ \&Santeria, $table ] );
    $table->bind( 'Tk::Label', '<1>', \&Santeria );

#~ use Tk::WidgetDump; $mw->WidgetDump;
    MainLoop;
} ## end sub Main

__END__
[download]

You could also iterate in other Tk::Table ways, maybe even on $table->{Rows}

Another way, keep track of the selected widget, since it belongs to $table

my $last = $table->{last_selected};
$last and $last->configure( -background => 'white' );
$w->configure( -background => 'grey' );
$table->{last_selected} = $w;
[download]

I know what you're thinking, if you're going to do that, you should subclass Tk::Table, and add a destructor where you clean up these extra keys... :D