FS36280 is the right reference for a brand new aircraft but be careful!!! Two years ago, during 75th birth of 51st Wing open day, 5 AMXs were on static display. You could see 5 different shades of grey. On the following link you can also see a comparison with a Tornado and a Eurofighter.
http://www.eaf51.org/Foto_Istrana_75_Mostra_Statica.htm
Lighter gray, Bluish darker gray, slighty tan gray...
My opinion: defining the correct Federal standard is nearly impossible . AMXs of 32nd wing based in Amendola have different shade of gray than 51st wing's AMX based