Yejing Liu, Hao Wang, Jinfa Ho, Ryan C. Ng, Ray J. H. Ng, Valerian H. Hall-Chen, Eleen H. H. Koay, Zhaogang Dong, Hailong Liu, Cheng-Wei Qiu, Julia R. Greer, Joel K. W. Yang
In a report recently published in Nature Communications, a research group led by Associate Professor Joel Yang from the Singapore University of Technology and Design (SUTD) printed probably the smallest colourful 3D model of the Eiffel Tower. Impressively, no pigments or inks were used. Instead, the 3D-printed model of the Eiffel Tower, measuring less than half the width of a human hair at 39 micrometers, exhibits multiple colours due to the manner in which light interacts with the nanostructures that hold up the model. The 3D models are made of a finely printed mesh of transparent polymer, forming photonic crystals. These mostly hollow designs remarkably shrink down in size by about 5 times when heated to produce a wide range of colours.
You can find more details at https://www.sutd.edu.sg/Research/Research-News/2019/10/Structural-colour-printing-of-3D-microscale-object