Combined answers:
# https://unix.stackexchange.com/questions/140610/using-variables-to-store-terminal-color-codes-for-ps1/140618#140618
# https://unix.stackexchange.com/questions/124407/what-color-codes-can-i-use-in-my-ps1-prompt
# \033 is the same as \e
# 0;32 is the same as 32
CYAN="$(echo -e "\e[1;36m")"
GREEN="$(echo -e "\e[32m")"
YELLOW="$(echo -e "\e[33m")"
RESET="$(echo -e "\e[0m")"
# https://stackoverflow.com/questions/4485059/git-bash-is-extremely-slow-in-windows-7-x64/19500237#19500237
# https://stackoverflow.com/questions/4485059/git-bash-is-extremely-slow-in-windows-7-x64/13476961#13476961
# https://stackoverflow.com/questions/39518124/check-if-directory-is-git-repository-without-having-to-cd-into-it/39518382#39518382
fast_git_ps1 ()
{
git -C . rev-parse 2>/dev/null && echo " ($((git symbolic-ref --short -q HEAD || git rev-parse -q --short HEAD) 2> /dev/null))"
}
# you need \] at the end for colors
# Don't set \[ at the beginning or ctrl+up for history will work strangely
PS1='${GREEN}\u@\h ${YELLOW}\w${CYAN}$(fast_git_ps1)${RESET}\] $ '
Result: