Trust the Sheriff to find a fine full colour example of the sg156 Orange.
We do, occasionally, delve into debates on colour, richness, tones and densities etc, but this stamp is a prime example of "how difficult it is, often" to fairly represent "the stamp in front of you".
For example, here are some file pictures of sg156.
sg 156 exhibiting "A range of shades"
Now, the three on the left are actually all the same stamp, as listed by eBay, a reputable auction house, and a PTS dealer. I'm not saying which is which, but the top exhibit has a yellow cast, and the bottom exhibit has a blue cast (central one is about neutral), so you can see that a knowledgeable stamp buyer still has to make a colour judgement, even when a clear scan is shown.
I then placed four examples on the same stock card, and scanned them in a single pass.
Note the colour of this stamp appears darker "against a darker background", and lighter "against a lighter background".
Four SG 156 GB 9d Orange Examples.
Going to Google doesn't help to establish "definitive colour", either ...
Google examples of GB SG 156 8d Orange
And even a professional auction house, using the same scanning equipment, on consecutive lots in an auction, will not achieve a reliable "colour reference point"....
Sandafayre Lots - GB SG 156 Orange
Some judgement is still clearly required. (Although hopefully you can see some consistency between the Sheriffs example on paper, my example on paper, and Sandafayres example on paper).
Its when they come off paper that the most colour variance starts to creep in.
The 8d, in its day, paid for a letter to Australia, a registered item to Europe, or a chunkier item sent within the UK.
Your example, unless its toning creeping into the equation, looks like it may have come off brown backing paper when soaked off. That gives it a darker tone, which favours the blue end of the spectrum.
Here are the slivers I referred to earlier ....(Yours is in the middle).
SG 156 - Query Item - SG156a
I stand by believing yours is SG 156 on two counts ....
1) Whilst there is a superficial match to right, the orange tones, on top of the yellow tone contained in the substrate, favour it being a SG156.
2) There are only four sheets of SG156a known (with only two stamps currently known in used condition), but in every SG156a I've seen, the perforations all favour narrow left margins (ie the printed centre is always to the left of stamp, or central). The only place I've encountered a right bias, like yours, is amongst the SG 156 population, where numerous examples exist.
May not be good news today, but at least you know what to look out for (and how to mentally adjust what you see)!!