fs_mgr: adb-remount-test.sh: use 24-bit forground colors

This allows colors to rendor according to user preferences
in terminal emulator settings.

Signed-off-by: Mark Salyzyn <salyzyn@google.com>
Bug: 161454607
Test: make sure colors make sense
Change-Id: Ie2749dcce66954deddbca2863dadfa270cc6633e