gvcolor: 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 CentOS possible default full paths are:

/usr/bin/gvcolor - from package: graphviz

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/gvcolor - from package: graphviz

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

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