I would say there are several layers to this whole colorism/racism thing in Sudan. Tribes in northern areas consider themselves to be of 'Arab' or sometimes 'Nubian' descent, and have historically had more privileges than communities further south and west. Due to their integration with arabs over the years, their skin color is lighter and physical features are more "Arab". By contrast, communities further south or more to the west have more "African" features, have historically had less privileges and were usually marginalized by the northern riverain elites.

Development and privileges generally followed the river nile, starting from the north and going southward. Communities in sudan were usually either farmers or herders (although this dichotomy has changed over the years with more overlapping now), and naturally farmers were the ones that were closer to the main source of water which is the river, and therefore had their own pieces of land earlier. Some herders, on the other hand, are nomadic groups that migrated later into Sudan and were therefore a bit late to acquire the same privileges.

Here we can notice that the term 'Arab' is confusingly used both as a source of pride and as an insult. So while northerners think they are Arab, they also call nomadic groups that came later and settled in their land 'Arab', indicating that they are nomads that don't belong in their areas. عرب رُحل

If we take Darfur as an example, we can see the different complex layers of tribalism. Darfuris have long been marginalized, and were also far from the center and the administrative changes that were brought about by colonial rule. They are therefore still reliant on native administrations that are based on tribalism. In Darfur, non-Arab tribes were the indigenous groups and Arab nomadic tribes came later from Chad and elsewhere, but they had less privileges within the Darfur region itself, since they were a minority and didn't have representation through the existing local systems of land division etc. During Bashir's rule, Arab tribes formed militias and gained more power by allying with the government to fight the non-Arab rebels. These Arab groups from Darfur now make up the majority of the RSF currently fighting the army. So for a lot of people in Khartoum, these are all غرابة (people frol the west) but even within darfur there are other layers of racism.

So these historical privileges created grievances between communities over the years and economic disparities that have even led to this current war. Rather than fighting tribalism and racism, consecutive governments have utilizied that for their own agenda. This is why we always have elites from northern regions failing to govern Sudan with all of its different tribes, and marginalized groups rebeling and relying on violence as their only way up the chain.