Perak 1957 Colour Question

Here is a pair of apparently the same stamp: a 1957 Perak.
Scott only lists a chocolate while the right-hand stamp is definitely NOT chocolate.
There is too much red/violet in it for it to be simply chocolate.
Could someone with a Gibbons please take a quick look and tell me if there is some special notation next to this particular issue?
Thanks in advance.

G'day Tony,
yes a common occurrence for Perak collectors,
we have:
SG155 10c deep brown 4th aug 1957 10p GBP
SG156 10c deep maroon 21st feb 1961 10p GBP

easily spotted in multiples, on their own they can
be misinterpreted. well spotted

The difference being so obvious why wouldn't Scott make some note about it?
Silly question, I know.
You know, other than 4 countries which I collect completely I collect all else only up to 1960.
If I were younger I would consider getting myself a complete worldwide Gibbons from the 70s or 80s or whenever, except that I don't have the energy to go through some 50 albums and reorganize the entire mess to a new system.

I know where you are coming from, I am chained to Stanley Gibbons
but I really like the Scott catalogue format, and the font used by Scott,
I find reading Scott is a pleasure, more so than Gibbons, but I am sure
they both have their failures.
The Gibbons "door-step" catalogues are a lump of a thing, just to
get them on and off of the Bookshelf. They are spineless, and droop
and curl if you ever tried to stand them up, (only seen this way
at Libraries :)

If I were beginning again now, I would (if I understand correctly)
that Michel is now in the English Language, I would go for their
system of numbering. Casting dignity aside, I want all my stamps
catalogued, the dunes, the appendices etc, it should be left to
the collector to determine what is admissable.

SG is the only reference for me for Commonwealth material, especially when it comes to pesky shades and perf varieties. Scott fails in that area, whereas it excels in US listings, which is to be expected.

I also find the Scott system of dividing stmps up into types (semi-postal, airs etc), rather than listing chronologically, takes a lot of getting used to.

I love Michel although my Germany Specialised is in German, which I can't read but can sort of figure out.

I have Scott on CD, and no SG world catalogue. I'll get one one day I suppose, but %600 is better spent on stamps IMHO