Do you know, I'm really not sure. The level of my research amounts to reading the odd Osprey book and looking at pictures of how other people have painted them

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Green feathers may equate to light flank troops and red and white to centre or " hat" troops and possibly pure red or white to the Grenadiers, however that's based more upon my Napoleonic reading than AWI.
My take on it is that this particular Regiment had been in America since the start and would have contained a high proportion of veterans and been involved in a number of major campaigns. Their uniform would have been altered to take in the extremes of climate in the Southern campaign and mixed in with veterans hanging on to old bits of kit and new intake turning up in newly issued uniform, even in the same company not everybody's uniform would look the same so I'm not to fussy about how they are portrayed.
The important thing for me is that I will be able to tell the difference on the table top between the Welsh lads and the Guard light companies, because the 23rd will have the three white feathers and the Guards will have a single green feather
