Need help identifying this one

That's what's confusing me.

It might be the bright scarlet color shade, which is listed in Stanley Gibbon as #220, but not listed in Scott. In Stanley Gibbons, is priced the same as the scarlet stamp. Scott does list a GB #128h (rose carmine) which is listed in the SG GB Specialised, but I don't think your stamp is that color shade. Keep in mind, IDing these color shades on a computer monitor isn't reliable without a reference color shade stamp in the same picture.

The year on the postmark does appear to be 02 (i.e., 1902).

This is the same with a flash

Your second pic looks like the normal scarlet on my screen. When taking camera pics, it needs to be done in "natural" light (i.e., closest equivalent to sunlight).

Since the year of the cancellation seems to be 0?, it must be a De La Rue stamp. The Stanley Gibbons Specialised Catalogue lists four shades.
The stamp with "specimen" overprint is a scarlet one. It is jus having tea with the deep bright scarlet one.

I'm sad to say that I can discern no difference in the colors of any of these stamps even when a scan like this one placing them next to each other should make it obvious. This has been and continues to be a problem for me with many issues.