use v5.12;
use warnings;


while ( <DATA> ) {
    chomp;
    say "'$_'";
    say $3 while                # print 3rd capture
      $_ =~ /(^|\s)                # starts with line's start or whitespace
             ("?)                  # capture optional double-quote inside (otherwise empty string) 
             ([^\2]*?)             # capture anything non-quote 
             \2                    # end with same quote 
             (?=(\s|$))            # look-ahead at following whitespace or line's end
            /xg                    # g= loop _globally_ over all matches   x=allow multiline extended regex
}




__DATA__
50 0 "R0 G255 B0 A255" "Solid" 118 1 "R0 G0 B0 A255" "R0 G0 B0 A255" 0
70 0 "R0 G255 B255 A255" "Solid" 118 1 "R12 G12 B12 A255" "R12 G12 B12 A255" 0