Disclaimer: The following is in no way intended to be an accurate representation of any colour carried by any regiment of the British Army at any time; merely my own imaginings.
Loudon's Highlanders:
Raised by John Campbell, 4th Earl of Loudoun, at Culloden commanded by Lt. Col.John Campbell, 5th Duke of Argyll.
King's Colour, the Great Union unadorned. Choice of regimental colours, first is a plain Campbell of Loudon. As the regiment was only raised in 1745, decided to have the choice of another following more the guidelines which ended up incorporated in the Warrant of 1751. The emblem is the Thistle Garter containing the Royal Cypher of George II, surmounted by the crown (used the one which came with the cypher for simplicity). There seems to be some disagreement as to the facing colours of Loudon's; a portrait of 1747 shows Loudon in buff, Millan in his list of 1745 says white. So Buff or white Regimental Colour, personal choice prevails.
Barrell's:
The easy one.
The "Old Buffs":
In 1744 the Regiment was then under the command of Lieutenant-General Thomas Howard, the 2nd Earl of Effingham. The Regiment was commanded at Culloden by another Howard. So, I've used the crest from the Effingham Achievement of Arms as the colour badge. The small size of the badge on the King's Colour is deliberate as it seems that when artists illustrated colours at this time, they deliberately exaggerated the size of the badges to aid identification. Hence on Barrell's, the badges are usually shown huge.
Sackville's:
Commanded at Culloden by George Germain, 1st Viscount Sackville, the badge is the crest from the Sackville Achievement of Arms.
Tools: MS PowerPoint and Paint. Photobucket.
No more planned at present, project in mind was small anyway.