I find this problem a lot with lots of different programs. I don't
use sqlplus, but I'd try this:
export TERM=xterm
This fixes color problems, etc.. If you don't use bash, then you'll
have to do something else of course :) But set your term type
(environment variable) to xterm, and it should fix all your
problems. If not try TERM=ansi
Hope this helps,
-Craig