This will look like this but username, @-symbol, hostname, workdir, and $-symbol differently colored.
🐳 username@hostname:/workdir$
# defining a custom PS1 as build argument
ARG CUSTOM_PS1="'🐳 \[\033[1;36m\]\u\[\033[1;31m\]@\[\033[1;32m\]\h:\[\033[1;35m\]\w\[\033[1;31m\]\$\[\033[0m\] '"
# Only append if not empty
RUN [ -n "${CUSTOM_PS1}" ] && echo "PS1=${CUSTOM_PS1}" >> $HOME/.bashrc