Right, I think I've got a bit figured out on the bitfields. However, this doesn't work as expected:

use constant AS_BG    => 0;
use constant AS_FG    => 8;
use constant AS_U     => 16;
use constant AS_BLINK => 17;
use constant AS_BOLD  => 18;

my $test = 0;

#$test |= ($v << $k);  # set $k to $v
#$test &= ~($v << $k); # 
print "Test0:[$test]\n";
$test |= 41 << AS_BG;
$test |= 31 << AS_FG;
$test |= 0 << AS_U;
$test |= 0 << AS_BLINK;
$test |= 1 << AS_BOLD;
print "Test1:[$test]\n";
print "Test parts: ".($test >> AS_BG).", ".($test>>AS_FG).",".($test>>
+AS_U).",".($test>>AS_BLINK).",".($test>>AS_BOLD)."\n";
[download]

Output:

Test0:[0]
Test1:[270121]
Test parts: 270121, 1055,4,2,1
[download]

Now, I'm sure I'm missing something here - but what? :-)