while (my $ref = $sth->fetchrow_hashref ()) {

    ### NEW CODE ###
    # Start up a new query
    $clref = $dbh->prepare ("SELECT color FROM colors WHERE item_id = ".$ref->{item_id});
    $clref->execute;
    # Push each new colour onto the array referenced by
    # $ref->{color}
    while (my $color = $clref->fetchrow_hashref()) {
        push @{$ref->{color}}, $color->{color};
    }
    # Now $ref->{color} is an arrayref full of colours.
    ### ### ### ###

    my $serve_url = sprintf ("serve_image.cgi?item_id=%s;picture", escape ($ref->{item_id}));  

    # generate a form allowing a quantity of the item to be added
    # to the cart
    push (@row, 
        start_form(-method=>'POST', -action=>url())),
        hidden( -name => "choice", -override => 1, -default => "add" ),
        hidden( -name => "item_id", -override => 1, -default => escapeHTML($ref->{item_id})),
        Tr ({-style=>"font-family: verdana; font-size: 10pt;"},
            td (
                img ({-src => $serve_url, -alt => escapeHTML($ref->{item_id})})
            ), 
            td ({-width=>"80", -valign=>"top", -align => "center"}, 
                escapeHTML( $ref->{item_id} )
            ),
            td ({-width=>"190", -valign=>"top"}, 
                escapeHTML( $ref->{description} )
            )
        ),
        Tr ({-style=>"font-family: verdana; font-size: 10pt;"}, 
            td ({-colspan => "3", -align => "right", -style=>"font-weight: 700; color:blue;"}, 
                "Price:  \$", 
                escapeHTML( 
                    sprintf( "%.2f", $ref->{price})
                )
            )
        ),
        Tr ({-style=>"font-family: verdana; font-size: 10pt;"}, 
            # Here is where you need to RTFM. At this point,
            # $ref->{color} is an arrayref. I suspect that
            # the popup_menu procedure will accept an array
            # reference as an argument, but I'm not sure.
            # Also, I'm too lazy to RTFM myself :o) In any
            # case, if you need to give it an array instead
            # you can dereference the arrayref. Check the 
            # links below for how to do that.
            td ({-colspan => "3", -align => "right"},
                "Colors:", 
                popup_menu( -name => "color", -values => $ref->{color})
            )
        ),
        Tr ({-style=>"font-family: verdana; font-size: 10pt;"}, 
            td ({-colspan => "3", -align => "right"},
                "Quantity:", 
                popup_menu( -name => "quantity", -values => ["1", "2", "3", "4", "5", "6", "7", "8", "9"])
            ),
            td (
                image_button( -name => "Add Item", -src=>"../images/add.jpg", -border=>"0" )
            )
        ),
        Tr ({-valign=>"top"},
            td ({-colspan=>"7", -width=>"100%"}, 
                hr
            )
        ),
        end_form()
    );
}