Multi-layer coating film forming method

A method of forming a multilayer coating film, comprising:

• (1) applying an aqueous first colored paint (X) comprising a color pigment (x1), an effect pigment (x2) and an acrylic resin on an object to be coated to form a first colored coating film;
• (2) applying an aqueous second colored paint (Y) comprising a viscosity modifier (y1), a color pigment (y2), an effect pigment (y3) and an aqueous acrylic resin dispersion on the first colored coating film to form a second colored coating film;
• (3) applying a clear paint (Z) on the second colored coating film to form a clear coating film;
• and
• (4) heating the first colored coating film formed in step (1), the second colored coating film formed in step (2), and the clear coating film formed in step (3) simultaneously to cure the coating films, wherein
• a solid content of the aqueous second colored paint (Y) is in a range of 0.1 to 6 mass %,
• a dry film thickness of the second colored coating film is in a range of 0.2 to 3.0 μm,
• an average value of light transmittance of the second colored coating film at a wavelength of 400 nm or longer and 700 nm or shorter is 1% or lower, and
• a difference |R(X)−R(S)| between an average value (R(X)) of light reflectance (110°) of the first colored coating film at a wavelength of 400 nm or longer and 700 nm or shorter and an average value (R(S)) of light reflectance (110°) of the multilayer coating film at a wavelength of 400 nm or longer and 700 nm or shorter is 5% or lower.