my $step = 0;
my $str = "";
my $color;
my $range = { "min" => 130, "max" => 230, "steps" => 50 };
my $curr;

# ... omissis ...

while($node = $csr->fetchrow_hashref)
{
	# ... omissis ...

	$curr = $$range{max} -
		(($$range{max} - $$range{min})/$$range{steps}) * $step;
	$curr = sprintf("%02x", $curr);
	$color = "#" . $curr . $curr . $curr;
	$str .= "<tr bgcolor='" . $color . "'><td>" # ... omissis ...

	# ... omissis ...
	
	$step++;  
}