Tip: if your grep outputs colour, the command is aliased to something like grep --color=auto. You can check with the alias command.

There's nothing wrong with that, until you start using pipe (|) to use grep's output in other commands. The --color switch adds ANSI characters for colour and this can have unexpected results.

To be safe, unset the alias (check ~/.bashrc, ~/.profile or one of the other files that's sourced on login) or run \grep. The \ in front of it will run the actual command, not the aliased command.