rainbow-easy: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/sbin/rainbow-easy - from package: rainbow

You may install the required package with command apt-get install {package}

Error in other languages:
rainbow-easy: bevel nie gevind nie
rainbow-easy: comandă negăsită
rainbow-easy: comando não encontrado
rainbow-easy: commande introuvable
rainbow-easy: command not found
rainbow-easy: käsku ei ole
rainbow-easy: không tìm thấy lệnh
rainbow-easy: komanda nerasta
rainbow-easy: Kommando nicht gefunden.
rainbow-easy: kommandot finns inte
rainbow-easy: komut yok
rainbow-easy: nie znaleziono polecenia
rainbow-easy: níor aimsíodh an t-ordú
rainbow-easy: no se encontró la orden
rainbow-easy: no s'ha trobat l'ordre
rainbow-easy: opdracht niet gevonden
rainbow-easy: parancs nem található
rainbow-easy: perintah tidak ditemukan
rainbow-easy: príkaz nenájdený
rainbow-easy: příkaz nenalezen
rainbow-easy: команда не найдена
rainbow-easy: командата не е открита
rainbow-easy: 命令找不到
rainbow-easy: コマンドが見つかりません