掉色 (diào shǎi) is a separable verb (离合词) meaning 'to lose color' or 'to fade'. It is used for fabric, paint, hair dye, and other dyed materials. Because it's a verb-object compound, when you add a time duration, frequency, or complement, the two syllables split: you insert elements between 掉 and 色, e.g., 掉了一次色 ('faded once'), 掉完了色 ('finished fading'). You cannot place a direct object after 掉色; instead, the object comes before the verb as the topic (e.g., 这条裙子掉色 'this skirt fades').