Transmission spectrum of WASP-33 b and retrieved models. The blue and black circles represent transit depths from OR1 and OR2, respectively. Horizontal lines indicate the size of the wavelength bin. Error bars are at the 1-σ level. The red curve shows the retrieved median model and the 1-σ and 2-σ confidence envelopes are shown by the shaded regions. The gold diamonds show the binned median model at the same resolution as the data. The spectrum shows a feature from ~450 to 550 nm that is explained by the model spectrum including AlO.