Within cat EOF syntax you can just use variables and commands as well. Just tested it and I see the problem here. The EOF syntax will not interpret the backslash and print them literally. So those variables would require to be interpreted with echo -e first. I never used colors in this syntax before. It's up to you which syntax you prefer, some people still like the series of echos over cat EOF.

BOLD='\033[1m'
RESET='\033[0m'
BOLD=$(echo -e "${BOLD}")
RESET=$(echo -e "${RESET}")

help_options() {
  cat %%EOF
options:
  -h ${BOLD}show help and exit${RESET}

  $(date "+%Y-%m-%d")
EOF
}

help_options