Using map allows for code that is (IMHO) somewhat clearer and more concise.

sub cmyk2rgb {
    my ($cyan, $magenta, $yellow, $black) = @_;
    my $white = 255 - $black;

    use integer;
    return map $_ > 255 ? 0 : 255 - $_
        => map $_ * $white / 255 + $black
        => ($cyan, $magenta, $yellow);
}
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— Arien