E124 is a (red) food coloring agent which can be made in a variety of different ways. Generally it’s a synthetic compound made of Coal Tar as well as azo dye, both of which are always vegan in origin.
It’s not to be confused with E120, which is another red food coloring agent which vegans should avoid for a variety of reasons.
Unfortunately E120 is more common than E124 as E124 doesn’t remain stable in sour/acidic substances, and thus E120 (carmine) is often used in place of it when it comes to candies.
Wait, so is E124 Vegan?
Well, E124 is generally made from synthetic compounds that don’t involve or entail animal exploitation or animal-derived ingredients to be used. However sometimes E124 is made from Cochineal Red A, via crushed beetles, so if you see that in the ingredient list then it’s not vegan-friendly. Ultimately it may or may not be vegan-friendly, so if you want to be safe avoid it — but generally it is vegan-friendly. Just not always — in candy it’s often non-vegan, in other things it generally is.