The placement of Δώδεκα between the definite article and στοιχειώσεσί leads me to interpret ταῖς Δώδεκα στοιχειώσεσί as "in The 12 Principles/ Elements."
I just realized that that capital Δ delta wouldn't be in the original manuscripts. They were all "capital" letters in the early scripts. So, those "twelve basics" could simply have been part of another work, say a list of 12 foundational principles within Epicurus's On Nature. Literally, all that scholiast wrote was:
ΤΟ ΔΕ ΧΡΩΜΑ ΠΑΡΑ ΤΗΝ ΘΕΣΙΝ ΤΩΝ ΑΤΟΜΩΝ ΑΛΛΑΤΤΕΣΘΑΙ ΕΝ ΤΑΙΣ ΔΩΔΕΚΑ ΣΤΟΙΧΕΙΩΣΕΣΙ ΦΗΣΙ
followed by - and these need not be included within the 12 the way the sentences are written - "Also they are not of every size; no atom has ever been seen by our senses."
ΕΝ in this case with the dative can mean simply "within, among" so if Epicurus is talking about 12 fundamental principles or giving a summary of something that includes 12 items within one of his works, that would still be ΕΝ ΤΑΙΣ ΔΩΔΕΚΑ ΣΤΟΙΧΕΙΩΣΕΣΙ "among the 12 fundamentals."
Yeah, I'm not seeing this as "12 volumes" but rather as a summary of something with 12 items. Whether it's physics or sensation or the Canon or something else that needs to mention that color is a product of the arrangement of atoms, there's no way to tell from the context in Diogenes Laertius.
