Some of the most dramatic moments in Game of Thrones involved wildfire, but The Art Of Game Of Thrones reveals that it wasn’t originally going to be green. Wildfire is a mystical substance in the Game of Thrones universe that is created by the Alchemist’s Guild; it’s a green, glowing liquid in the series, and when it’s lit, it burns hotter than any other fire and is near-impossible to put out. It’s also wildly unstable and dangerous, which is why it’s rarely used, even in the war-mad times of Game of Thrones.

However, wildfire does show up a few times in the series; to destroy Stannis Baratheon’s (Stephen Dillane) fleet in the Battle of the Blackwater, and again to destroy the Sept of Baelor. These two scenes are some of the most dramatic in the show, when the audience is treated to visions of a fleet going up in neon green flame, and an explosion that levels one of the largest buildings in King’s Landing. However, these scenes could have looked very different, had the flames been the same red and orange as any other fire in the show.

One of the recently-released companion books for the series, The Art of Game of Thrones, reveals early concept art of the Battle of the Blackwater, and in all the images, the wildfire is red/orange. Imagery of the destruction of the Sept is not included (although concept art for the Sept itself is), but a description of the images makes note of the fact that this is wildfire, and it was originally a different color.

Had Game of Thrones gone ahead with this change, it would almost certainly have been a mistake. For one thing, the books themselves describe wildfire as “emerald green”, and that burning can even make the air around the fire appear green. While Game of Thrones made many changes from the books, this kind of detail seems like a strange one to alter for no real reason. More than that, though, the color of the wildfire makes it distinctive, and shows exactly what kind of fire is being used.

If Sept’s destruction looked like any other fire, it could have been easy for Game of Thrones viewers to miss exactly what Cersei’s (Lena Headey) plot was - and the vitally important comparisons to the Mad King, who stockpiled wildfire under the city for this very purpose. Interestingly, the book does also include concept art for the scene right before the Sept is blown up, where barrels of wildfire are under the city, and here the substance is green, although presumably this art was created much later, once the color decision had been made.

The Art of Game of Thrones includes a slew of other details that nearly made it into the show - such gondolas to ferry people to the Eyrie, details of those things that did, and floor plans for many of the castles and ships. While it’s clear that some of the elements included (and excluded) were done for the sake of budget constraints or simply because a better option presented itself, it’s good to know that even though Game of Thrones was happy to change major plotlines, this was one detail that stayed true to A Song Of Ice And Fire - even though the change was at least briefly considered.

Next: Game Of Thrones Theory: Robin Arryn Is Littlefinger’s Son

The Art of Game of Thrones is now available from Insight Editions/HBO.