#!/bin/bash

if [ -n "$1" ]; then
    cols=6
    offset=-15
    colors=({16..255})
else
    cols=8
    offset=1
    colors=({0..15})
fi

for i in "${colors[@]}"; do
    printf '\x1b[38;5;%dmcolor%03d\x1b[0m' "$i" "$i"
    [ $(((i + offset) % cols)) -eq 0 ] && printf "\n" || printf " "
done