3D printed material having color and/or reflectivity control

A method for producing a 3D item by means of fused deposition modeling using a fused deposition modeling 3D printer comprising a printer nozzle, wherein the 3D item comprises one or more layers of 3D printed material, the method comprising a 3D printing stage comprising:

• providing 3D printable material to the printer nozzle, wherein:
• the 3D printable material comprises 3D printable core material, 3D printable first shell material and 3D printable second shell material;
• the 3D printable core material comprises a core thermoplastic material having a core thermoplastic material melting temperature Tmc1;
• the 3D printable first shell material comprises a first shell thermoplastic material having a first shell thermoplastic material melting temperature Tms1;
• wherein Tmc1>Tms1;
• the 3D printable second shell material comprises a second shell thermoplastic material having a second shell thermoplastic material melting temperature Tms2;
• wherein Tmc1>Tms2>Tms1;
• the 3D printable first shell material has a 3D printable first shell material optical property, the 3D printable core material has a 3D printable core material optical property different from said 3D printable first shell material optical property;
• controlling a temperature Tdm of the 3D printable material in the printer nozzle according to a scheme wherein during a first time period tp1:
• Tms2>Tdm>Tms1 applies and wherein during a second time period tp2:
• Tmc1>Tdm>Tms2 applies.