CBP applies the General Rules of Interpretation, which require classification in the most specific applicable provision before resorting to a residual. A colorant should be tested against the named dye classes (basic, direct, vat, reactive, solvent, pigment, etc.) and the fluorescent brightener subheading before defaulting to 320490. Importers should retain technical documentation — including Colour Index designation, ionic character, and application method — to support the classification decision.

Section 301 tariff exposure depends on the country of origin, not the HTS heading alone. Synthetic organic coloring matters originating from China may be subject to Section 301 tariffs regardless of whether they classify under a named subheading or the NESOI residual at 320490. Importers should verify the current Section 301 list and any applicable exclusions for their specific product and origin before entry.