A method for forming a multilayer coating film, comprising: a step of applying an aqueous 2-package type first colored paint on both a metal member and a plastic member of an automobile outer panel so as to form an uncured first colored coating film; a step of applying an aqueous 1-package type white paint (Y-1) on the uncured first colored coating film obtained in the step so as to form an uncured white coating film; a step of applying an aqueous 1-package type interference color paint (Y-2) on the uncured white coating film obtained in the step so as to form an uncured interference color coating film; a step of applying a solvent-based 2-package type clear paint on the uncured interference color coating film obtained in the step so as to form an uncured clear coating film; and a step of heating the uncured first colored coating film, the uncured white coating film, the uncured interference color coating film, and the uncured clear coating film formed in the steps to at 75 to 100°C so as to simultaneously cure these coating films to form a multilayer coating film, wherein the steps to are sequentially conducted, wherein the aqueous 1-package type interference color paint (Y-2) contains a vehicle-forming resin and titanium oxide-coated synthetic mica, the aqueous 1-package type interference color paint (Y-2) containing 27 to 33 parts by mass of the titanium oxide-coated synthetic mica based on 100 parts by mass of the vehicle-forming resin, and having a paint solid content of 20 to 24% by mass, wherein the solvent-based 2-package type clear paint contains a hydroxyl group-containing acrylic resin and a polyisocyanate compound in a ratio of 1.5 to 2.0 equivalents of isocyanate groups in the polyisocyanate compound relative to 1 equivalent of hydroxyl groups in the hydroxyl group-containing acrylic resin, and the polyisocyanate compound contains a polyisocyanate compound having a uretdione structure and a compound of a trimer or more of diisocyanate in a mass ratio of solid content of 10/90 to 50/50, and wherein the multilayer coating film has a lightness in highlight (L* (15°)) of 125 to 130, a flip-flop (L* (15°) - L* (110°)) of 45 to 55, and a b-value in highlight (b* (15°)) of -2.0 to -1.0 when measured by a multi-angle spectrophotometer. a step of applying an aqueous 2-package type first colored paint on both a metal member and a plastic member of an automobile outer panel so as to form an uncured first colored coating film; a step of applying an aqueous 1-package type white paint (Y-1) on the uncured first colored coating film obtained in the step so as to form an uncured white coating film; a step of applying an aqueous 1-package type interference color paint (Y-2) on the uncured white coating film obtained in the step so as to form an uncured interference color coating film; a step of applying a solvent-based 2-package type clear paint on the uncured interference color coating film obtained in the step so as to form an uncured clear coating film; and a step of heating the uncured first colored coating film, the uncured white coating film, the uncured interference color coating film, and the uncured clear coating film formed in the steps to at 75 to 100°C so as to simultaneously cure these coating films to form a multilayer coating film, wherein the steps to are sequentially conducted, wherein the aqueous 1-package type interference color paint (Y-2) contains a vehicle-forming resin and titanium oxide-coated synthetic mica, the aqueous 1-package type interference color paint (Y-2) containing 27 to 33 parts by mass of the titanium oxide-coated synthetic mica based on 100 parts by mass of the vehicle-forming resin, and having a paint solid content of 20 to 24% by mass, wherein the solvent-based 2-package type clear paint contains a hydroxyl group-containing acrylic resin and a polyisocyanate compound in a ratio of 1.5 to 2.0 equivalents of isocyanate groups in the polyisocyanate compound relative to 1 equivalent of hydroxyl groups in the hydroxyl group-containing acrylic resin, and the polyisocyanate compound contains a polyisocyanate compound having a uretdione structure and a compound of a trimer or more of diisocyanate in a mass ratio of solid content of 10/90 to 50/50, and wherein the multilayer coating film has a lightness in highlight (L* (15°)) of 125 to 130, a flip-flop (L* (15°) - L* (110°)) of 45 to 55, and a b-value in highlight (b* (15°)) of -2.0 to -1.0 when measured by a multi-angle spectrophotometer.