Alicent's big House of the Dragon episode 5 moment is more important than it seems

gamesradar.com:

House of the Dragon episode 5 features a huge moment for Emily Carey's Alicent Hightower – and it's a lot more important than it might seem. The episode revolves around the wedding of Rhaenyra Targaryen (Milly Alcock) and Leanor Velaryon (Theo Nate), and it's also the last time we'll see Carey and Alcock in their roles before a time skip introduces Emma D'Arcy as Rhaenyra and Olivia Cooke as Alicent.

Now, before we go any further, be warned that the following will delve into show and book spoilers, so turn back now if you don't want to know what might be coming next in the series! 

If you're still reading, then you're ready for the spoilers. In episode 5, Alicent discovers that Rhaenyra and Ser Cristen Cole (Fabien Frankel) slept together. That means she knows Rhaenyra was probably lying to her in episode 4 when the princess proclaimed her virtue, and though Alicent doesn't know for sure that the rumor about Rhaenyra and Daemon's brothel tryst is true, the young queen believing her friend over her father Otto Hightower (Rhys Ifans) led to Otto losing his position as Hand of the King – which he openly blames her for, and then warns her that her children will be killed if Rhaenyra takes the throne. 

All of this pushes Alicent past her breaking point, and she arrives late to Rhaenyra and Laenor's wedding, interrupting a speech from King Viserys (Paddy Considine). It's a big, dramatic moment, and it's made even more significant by Alicent's choice of attire. She's wearing a vivid green dress, and it's revealed that the Hightower's beacon, when lit to call the banners for war, is green in color. That's already very ominous, then, but some context from George R.R. Martin's Fire and Blood book reveals why the moment is even