color_matrix: 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/bin/color_matrix - from package: libterm-extendedcolor-perl

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

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