Hi Kentcottage,
Without a scan, which would be helpful, it is difficult to be precise wrt what exactly you have, but my guess is that you've got a very early form of GB postal stationery which is called the "penny pink". Providing 1d of postal value and the color is most decidedly pink. Please see this example:

The penny pink was introduced following the failure of the Mulready and without my books at hand, can't recall many specifics. Also,printed postal franking on official postal stationery is referred to as a "indicia", not a stamp, which in this case is both printed and embossed
I am sure others with chime in with more details.
Best,
Larry