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Clown Toby Jug (large) Orange/red Hair D.5610
The very first clown Toby jug, designed by Harry Fenton was issued from 1937 - c.1942. The British Design Registry (copyright) Rd No 810520 also appears below the backstamp, showing that this design was copyrighted late in the year of 1936. The standard colorway for this first edition was orange (a) hair and a black lined ruff, with a multi-colored motley stick handle and white face. Production ceased, as did almost all art pottery in the Staffordshire potteries during World War II, and factories concentrated on the production utilitarian china under the orders of the War Department. So no clowning around at Doulton until well after the war.
Clown Toby Jug (large) White Hair D 6322.
This post-World War II version was issued from 1951 - 1955 and the main colorway was white hair and a (b) red burgundy ruff and a flesh tone face (to lend contrast to the white hair and white face paint), but it's with this model, the D6322 where we see all the variants. There is one super-rare colorway, that has a (c) plain white ruff. It's illustrated on pages 88 and 89 of Steve Mullins 'A Century of Royal Doulton Character Jugs'. There's also rare white hair, white ruff variant with (d) pink details, most likely a so-called "experimental". These are usually backstamped Royal Doulton "trial" or "sample". Here's another experimental with red hair, red ruff and (e) black & yellow face paint.
There's another one with (f) brown hair, red ruff and red cheek paint.
One with (g) brown hair, red ruff & white cheek paint, marked "Sample".
Another with (h) black hair, black ruff and green face paint.
And another with (i) gold hair and face paint.
This is probably not an exhaustive list as new variants appear from time to time on eBay that no-one knew existed. And, as is always the way with the decorative arts and the creative temperament, consistency is not a strong suit. However I do hope this gives you an overview of this particular Doulton character jug.
Please let me know if I can be of further assistance with this, I would be glad to.