## 2 Results  
The metasurface is composed of three aluminum nanorods on a silica film, and an aluminum film of thickness 90 nm is sandwiched between the silica film and substrate. The metal-insulator-metal structure enhances the overall reflection. Three nanorods are periodically arranged, and \(i\)-th rod is tilted by \(\phi_{i}\) where \(a_{i}\) and \(b_{i}\) denote horizontal and vertical dimension. Detailed geometric dimensions can be found in Figure 1. When the metasurface is illuminated by visible light source, localized surface plasmon resonances formed near the nanorods offer structured reflection spectrum with multiple dips. When the rods have a rectangle shape, the metasurface optically responds differently under incident polarization due to the anisotropic geometry. Especially if the rectangle has a high aspect ratio, it can be approximated as a dipole which interacts strongly with light polarized parallel to the oscillating direction. As the optical resonances can be shifted by changing geometric dimensions and the pitch of the rod, it is possible to design three different nanorods with different resonance wavelengths and selectively excite them by matching incident polarization to the dipole moment direction.  
However, since three dipoles cannot be mutually orthogonal in a plane, cross-talks between rods are unavoidable. Although 60\({}^{\circ}\) of relative direction between each rod minimizes the cross-talk, the direction of the rods also determines the periodic arrangement and hence the reflection spectrum. Therefore, directions of rods are set for desired resonance wavelength and the final dimensions of three rods are tuned through parametric sweep. The metasurface is then fabricated by electron-beam lithography and lift-off process. (See Materials and Methods section for details). A scanning electron microscopy (SEM) image of the sample is presented in Figure 1c.  
Polarization sensitive reflection spectrum and the corresponding colors are presented in Figure 2. We used the Lumerical finite-difference time-domain (FDTD) solution for numerical simulation. The simulated reflection spectrum indicates that the metasurface has multiple peaks and dips over the visible range, especially 450 nm, 540 nm and 620 nm. At those resonance wavelengths, incident light may or may not excite the nanorods, and the spectra show notable distinction dependent on the polarization direction. Three distinctive nanoantennas provide active color generation sensitive to the incident polarization. As the polarization rotates from 0\({}^{\circ}\) to 180\({}^{\circ}\), the color gamut represented in CIE 1931 space forms an oval. Although the metasurface does not produce vivid primary colors, it covers a wide range of colors in a single design. Colors generated by the fabricated sample are measured by a CCD camera implemented in a hyperion 1000 microscope (bottom panel in Figure 2c).  
Figure 1: (**a**) Schematic of metasurface and (**b**) its unit cell. It has metal-insulator-metal structure where aluminum and silica are used as metal and insulator respectively on a silica substrate. Thickness of aluminum film, silica film and aluminum rods are 90 nm, 100 nm and 40 nm respectively. Three nanorods numbered by 1, 2 and 3 are periodically arranged and the unit cell has two of each of the nanorods. \(i\)-th slit is tilted by \(\phi_{i}\) where \(a_{i}\) and \(b_{i}\) denote horizontal and vertical dimension. Geometric parameters indicated in the figure are: \(p_{x}=500\) nm, \(p_{y}=500\) nm, \(a_{1}=180\) nm, \(a_{2}=120\) nm, \(a_{3}=100\) nm, \(b_{1}=40\) nm, \(b_{2}=70\) nm, \(b_{3}=60\) nm, \(\phi_{1}=0^{\circ}\), \(\phi_{2}=80^{\circ}\), \(\phi_{3}=130^{\circ}\). (**c**) Top view of scanning electron microscopy image.  
Figure 2: (**a**) Polarization dependent reflection spectrum, (**b**) CIE 1931 chromaticity diagram and (**c**) color palette. Simulated and experimentally obtained colors are shown in the first and second rows respectively. Polarization angle of incidence is represented in degree.