contrast: command not found

Have You tried accessing the binary with the full path?

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/lib/phylip/bin/contrast - from package: phylip

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