Ultraviolet spectral slopes (β), using the Calzetti dust extinction law, as a function of the observed UV magnitude at z ∼ 5 − 17, as marked. Lines represent the mean of the five runs with different seeds for each model; shaded areas represent the range between the minima and maxima shown by the 16^th and 84^th percentiles, respectively. Grey squares in the top left panel represent observational data from 677 galaxies at z ∼ 5, taken from Bouwens et al. (2014). As marked in other panels, we also show observational estimates of the β slope from recent JWST studies at z ∼ 7 − 17 (Castellano et al. 2023; Austin et al. 2024; Franco et al. 2024; Kokorev et al. 2024; Rinaldi et al. 2024).