Examples of images of the spectral index in various regions of the large Apertif-LOFAR image. The variety of spectral structures is evident. A few double-lobed radio galaxies showing the classical spectral structure are seen, while the emission from a star forming galaxy and from a cluster object is also present. Spectral indices commonly found in active radio galaxies (i.e. 0.5 ≲ α ≲ 1, see e.g. de Gasperin et al. 2018; Mahony et al. 2016 and references therein) are indicated by the light green to yellow colours. Flat or inverted spectra (α ≲ 0.5) are indicated in blue and light blue. Extremely steep spectrum and USS values are indicated in red and pink. The contours represent the LOFAR emission, and contour levels are from −0.55, 0.55 mJy beam⁻¹ (5σ) increasing in steps of 2. Negative contours are shown in grey.