londonSession = "0300-1200"
nySession = "0800-1700"
overlapSession = "0800-1200"
asiaSession = "1700-0300"
BarInSession(sess) => time(timeframe.period, sess) != 0
londonColour = #008000 
nyColour = #FF0000
overlapColour = #f57f17 
chartColour =  BarInSession(overlapSession) ? overlapColour : BarInSession(londonSession) ? londonColour :BarInSession(nySession) ? nyColour :na


EXAMPLE:

If(BarInSession(overlapSession)))
	SendTrade