The current header looks to be an original coloured image, although it may have been enhanced a little. It doesn't look like a coloured black & white to me.
It's interesting as it appears to show an Ariel in SCC No.2 brown, with the headlamp mask also in service colour and the headlamp clip and more particularly the handlebars cadmium plated. Contol levers seem to be unplated brass.
Is the uniform WRNS or is she Home Office or similar ?
The colour forum photo is from the book by J.B.Priestley "British Women Go To War" it shows his daughter Sylvia Priestley who was a W.R.N.S. despatch rider,the book contains 49 colour photos taken by P. G. Hennell most were taken inside factories,this one shows A.T.S. women drivers,its a nice book printed just after the war.
Interesting! The census number is largely hidden from view, but the first three numbers "155" are visible. From my Royal Enfield research I know that the Royal Navy census numbers passed the 10000 cape somewhere in 1941. Around the same time, the Royal Navy replaced the RN prefix by a RN suffix in the census numbers. This bike's color is SCC2, so it must have been built in 1942 or later. This would mean that the census number would be 155XX RN. The bike will also have had white tipped and white edged mudguards, which were typical for the RN motorcycles.
The female despatch rider has definately had a date with the magic pencil and most likely another with Mr P Brush.
As for the book, 49 colour photos in 1942 would have needed to be personally OKed by Churchill himself and funded by the Palace.
Really big pounds back then.
FWIW,
My mother was married in 1945.
All of her colour wedding photos were hand coloured.
They over expose the posative then it is like a childs colouring in book.
This remained a trade till the 90's when photoshop was commercially acceptable.
While there is a big stink about modern fashion photography being photoshopped to impossible proportions, it did not start with photoshop.
All fashion photos went in for retouching and when the touch up artist was finished they went back to the photo lab for a new negative to be made from the print.
Really really good artists could touch up the negs, good enough to be printed from, well to have seperations made from to be truthful.
We had a lot of them as clients when we started and by the time we closed the business it was direct digital printing .
This is one reason why I am always suspicious when I see "original period colour photographs " for sale as the colour chemical were not stable and unless he photo was laquered over to seal it would fade, particularly reds that continue to react eventually going brown.