Okay, a brief lesson on references: you can do anything to the array pointed at by a reference that you could do to the array itself. So, the following two snippets do exactly the same thing (one to an array, the other to a referenced array):

# create and fool around with an array
my @rray = ();
$rray[0] = "foo";
push @rray, "bar";
print $rray[1], "\n";
# prints "bar"

# create and fool around with an arrayref
my $arrayref = [];
$arrayref->[0] = "foo";
push @$arrayref, "bar";
print $arrayref->[1], "\n";
#prints "bar"
[download]

So as you can see, using an arrayref is just an indirect way of using an array, with the added benefit that the reference can be passed around like a scalar, and put into arrays and hashes, and all sorts of fun stuff like that.

So, back to your problem. You wind up with $ref (which happens to be a reference to a hash). You're already pulling out values like $ref->{item_id} and $ref->{description}, so now you need to make $ref->{color} an arrayref and iterate over it. Here's the part of your code that takes the record set and turns it into a table. The HTML looks kinda b0rked... Please forgive me if I screw it up more.

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 $serve_url = sprintf ("serve_image.cgi?item_id=%s;picture", esc
+ape ($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 => escape
+HTML($ref->{item_id})),
        Tr ({-style=>"font-family: verdana; font-size: 10pt;"},
            td (
                img ({-src => $serve_url, -alt => escapeHTML($ref->{it
+em_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-wei
+ght: 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/ad
+d.jpg", -border=>"0" )
            )
        ),
        Tr ({-valign=>"top"},
            td ({-colspan=>"7", -width=>"100%"}, 
                hr
            )
        ),
        end_form()
    );
}
[download]

For more information on references and how to use them (from people who know a whole lot more than me) See:
The 'references' tutorial by busunsl
References quick reference by tye

LAI
:eof