If you're a Harry Potter fan, you might be thinking “Aha, ze wrote 'truth potion' for the benefit of people who aren't familiar enough with the series to know the name 'Veritaserum'”. If you're a bigger fan, you might be thinking “But Veritaserum is as clear as water, and that potion isn't!” That's right! The real reason I don't say “Veritaserum” is because this is actually a modified version of Veritaserum that Granger invented. It is similar, but it is unaffected by the most well-known Veritaserum antidote, which is a tactical advantage.
A more cynical person might speculate that Granger invented it to circumvent legal restrictions on the use of Veritaserum, but the law usually refers to truth potions in general, and as the head of the Auror Office, Granger can get the necessary warrants easily.