local $/;
$_ = <DATA>;
1 while s#\[(\w+)[^\]]*\]\[/\1\]##ig;
print;

__DATA__
[b]bold text[/b]
[color=Red]Red text text[/color]
[color=Red][b]Red bold text[/b][/color]

I need to remove the ones below: 
[b][/b]
[color=Red][/color]
[color=Red][b][/b][/color]