Well, figure a) shows a ribbon representation of the fold (as helices and strands) of the protein 7QSW (https://www.ebi.ac.uk/pdbe/entry/pdb/7qsw) which is RubisCO (https://en.wikipedia.org/wiki/RuBisCO), an plant protein that plays a key role in photosynthesis.

The different colours are for the predicted and 'real' (ground truth) models. The fact that it is hard to distinguish is partly the - as you point out - weird colour choice, but also because they are so close together. An inaccurate prediction would have parts that stand out more as they would not align well in 3D space.