":aa2bb4cc6dd8" =~ / (:)
                     (?{ [] })   # initialize $^R
                     (?:
                         (\w\w) (\d)
                         
                         # add captures to $^R:
                         (?{ [@{$^R}, [$2, $3]] })
                     )*
                   /x;

dd $&;   #->  ":aa2bb4cc6dd8"
dd $1;   #->  ":"
dd $^R;  #->  [["aa", 2], ["bb", 4], ["cc", 6], ["dd", 8]]