They look like standard (Unixish) escape sequences to control formatting. I have little experience of the debugger, but looking at perldoc perldebug I notice this section:

       "ornaments" Affects screen appearance of the command line
                   (see Term::ReadLine).  There is currently no
                   way to disable these, which can render some
                   output illegible on some displays, or with
                   some pagers.  This is considered a bug.

Assuming this deficiency still exists in the code, and not just in the documentation, you may still take hope from the fact that substantial reworking of the debugger is ongoing for the development track of perl, and it is possible that now would be a good time for a carefully worded reminder (via perlbug) of the problem.

Hope this helps,

Hugo