NODE CREATION

#Create four nodes
set n0 [$ns node]
set n1 [$ns node]
set n2 [$ns node]
set n3 [$ns node]

$ns color 1 blue: is to set color of the packets for a flow specified by the flow id (fid). 

$n3 shape "square"
$n3 color "black"

$n0 shape "square"
$n0 color "blue"