As I understand from the wiki, glowing green sweat will be visible after opening the seventh gate (Gate of wonder/Gate of shock). But, why it was visible for Rock Lee, when he can open only 5 gates.
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The Anime does not always pay attention and replicate the same details from the manga.
The wiki is based on all Manga information whereas the pictures are generally from the Anime.
The author of Naruto, Masashi Kishimoto, primarily focuses on his manga while he let's other people create the Anime. From time to time, the makers of the Anime don't follow every little meticulous detail that Kishimoto has illustrated in his manga. In this case, the Anime Rock Lee starts glowing green early as a graphic effect even though he isn't supposed to yet.
Another example of this is when Danzou uses Izanagi. In the manga, he can sacrifice an eye for a 1 minute duration of the skill. In the anime, each blow he receives from Sasuke requires an eye sacrifice.
As you can see, the Anime isn't very diligent in their Naruto facts.