Alias⌗

See if there are any alias defined for ls on your terminal

alias

For me it was alias ls='ls $LS_OPTIONS' and LS_OPTIONS environment variable had a value of --color=auto

.bashrc⌗

Check the contents of your ~/.bashrc file. Generally, these aliases are defined here. Mine had these lines

export LS_OPTIONS='--color=auto'
eval "`dircolors`"
alias ls='ls $LS_OPTIONS'
alias ll='ls $LS_OPTIONS -l'
alias l='ls $LS_OPTIONS -lA'

Update export LS_OPTIONS='--color=auto' to export LS_OPTIONS='--color=never' and restart the terminal

export LS_OPTIONS='--color=never'
eval "`dircolors`"
alias ls='ls $LS_OPTIONS'
alias ll='ls $LS_OPTIONS -l'
alias l='ls $LS_OPTIONS -lA'

Also, take note of the other two helpful aliases.