it depends on the invocation, and by default it checks for tty or not. the aliasing often does not touch this.

example alias:

  $ alias ls
  ls='ls --color=tty'

and from ls(1): "With --color=auto, ls emits color codes only when standard output is connected to a terminal. The LS_COLORS environment variable can change the settings. Use the dircolors command to set it."

("tty" and "if-tty" are the same as "auto")