#!/bin/bash
trap ctrl_c INT
ctrl_c() { tput sgr0 && tput clear && exit 0; }

while true; do
  tput setab "${b:-0}"
  head -c "$(tput cols)" < /dev/zero | tr '\0' " "
  if [[ $b -gt 7 ]]; then b=1; else b=$((b + 1)); fi
done