Galaxy UV spectral slope, β_UV, as a function of redshift. The red points mark the JWST-PRIMAL sample from this work, and the shown quantities are all derived directly from the NIRSpec Prism spectroscopy. The yellow hexagons show the mean β_UV in bins denoted by the horizontal errorbars, and the vertical errorbars represent the 16th to 84th percentile of the distribution in the respective bins. The blue shaded region represents the minimum value β_UV = −2.6 to −2.4 for a standard stellar population with negligible dust and maximum nebular continuum contribution (see Sect. 3.4 and Cullen et al. 2024).