In the lore the Word Bearer's legion colors are described as being the red of dried blood and the fires of damnation. Trim is done with bare metal and black. This has resulted over time in artwork showing a bright crimson red, but in painting guides and EVERY army I could find online the paint scheme has been a dark brownish crimson. Now other armies have undergone evolution paint scheme wise over time, Ultramarines being a excellent example (They used to have a LOT of bright yellow trim), but the Word Bearer's paint scheme has been an oddity for over a decade in that in newer artwork their colors had changed but in painting guides and army books it was stuck in 3rd edition. Here is a run down of how things have evolved over time.
3.5 edition Chaps Space Marine Codex
Until Betrayal at Calth this has been the only non-Forge World release for Word Bearers from GW for 15 years. As you can see the paint scheme is a darker crimson that verges on brown or purple.
This was their established paint scheme for a LONG time.
Dawn of War
For me the most stunning (and only) depiction of Word Bearers models painted on their updated colors prior to Betrayal at Calth was in a DLC for the game Dawn of War 2. As you can see the armor is a bright crimson without any brown and it's visually impressive. It also does NOT make them look like Blood Angels.
This is the color scheme I was trying to emulate with my army. (poorly as I am not a skilled painter)
Word Bearers Novels
If you haven't read these READ THEM!!! They are VERY good books, especially book 3. Both the White Consuls and Word Bearers are so awesome and fleshed out that I found I was rooting for both sides.
These were the other "official" portrayals of Word Bearers from GW art wise for a decade. Their cover arts are each slightly different, but shadows aside the red is a brighter crimson.
Bright in shadow
Modern bright crimson
Again bright crimson
Forge World's Horus Heresy A.K.A. "The big reversal"
So between Dawn of War 2, the Black Library novel covers, and the total lack of Word Bearer releases from GW it seemed for a decade that the paint scheme had in fact changed. Then Forge World decided "nope" and they depicted Word Bearers in their old 3rd edition 'rust brown' Crimson armor.
Ok so apparently we didn't change from the old scheme, which to my eye is less visually interesting and lacks highlights.
The First Heretic
BUT WAIT!!! Then Black Library released "The First Heretic", again an awesome book, and they went BACK to the updated brighter color scheme. Ok, so now the colors have changed then.
The Gal Vorbak on the cover have the brighter crimson consistent with Dawn of War 2 and the other novels. But...
Forge World Word Bearers pt 2
Then Forge World released a second wave of Word Bearers models including these amazing Gal Vorbak models. Models painted in the OLD 3rd edition dark crimson scheme.
So that catches us up to now and the new hopefully final paint scheme.
Betrayal at Calth
So the Betrayal at Calth is the first new Word Bearer release from GW proper since their "daemon bomb" codex entry in the old 3.5 edition codex. I am hoping that it will be the paint scheme they will stick with into the future, as it looks stunning and does not look like Blood Angels to my eye.
What gives me confidence that the manic nature of the Word Bearers color scheme has come to an end is that we now have a new painting guide for them, so hopefully that means this one is here to stay.
Now I just need to buy all those paints...