McGill’s said the new liveries reflected “iconic local buses of the past”.
Services in Stirling and Falkirk area will be branded with a light blue and cream design as McGill’s Midland Bluebird.
Buses in West Lothian will be branded as McGill’s Eastern Scottish with a dark green and cream livery.
These are understood to have been based on the former state owned Scottish Bus Group’s colours for their operators, with the Eastern Scottish names used from the 1960s to 1990.
The sale has seen McGill’s take over First Scotland East’s bus fleet and depots in Larbert, Bannockburn, Balfron and Livingston, along with some 550 staff – increasing the McGill’s workforce by a quarter.
It has also acquired Edinburgh open top bus tour operator Bright Bus from First.
The sale follows McGill’s taking over Xplore Dundee, the city’s main operator, and operating cross-Border services for German operator FlixBus.
McGill’s Group chairman James Easdale said: “As witnessed following our recent deal for Xplore Dundee and in our partnership with FlixBus, we are determined to invest operationally to ensure our customers receive a service they value and can enjoy using.
“We believe in empowering local teams to deliver for their local communities rather than a centralised, top-down approach.
"We want passengers to have an affinity with their local buses and one step in that process is the introduction of iconic liveries for the fleet.”
McGill’s Group director Sandy Easdale said the company was still on the acquisition trail.
He said: “We have a clear vision for growth and profitability and we are able to conclude deals speedily and with the minimum of fuss.
"The opportunity to bring First Scotland East’s businesses into McGill’s was always an attractive proposition to us and it now gives us a presence across the central belt.
“Whilst others may be shying away from expansion given the unsettled economic picture, we are continually seeking new opportunities to invest in transport, construction and property.”
McGill’s Group chief executive Ralph Roberts said: “We will be examining every area of the business to revitalise our offering such as customer interaction, staff development and training, vehicle quality and local decision-making.
“One of our key priorities will be to invest in the fleet and bring down the average age of buses on the road.”