I’m working on a tutorial figure and going ok until I joined a mirrored mesh of fingers and arms. when I joined them the new mesh turned black. I somehow managed in the end somehow get it to not turn black, because I think I ended up skipping the mirror modifier I was told to apply…anyway short lived victory as then when I was told to re-mesh the now combined arms and fingers it all
went black again. It displays as such in object mode as well-cell shading it black. I’ve tried flipping the normals to outside but that doesn’t seem to do anything. Anyone have any thoughts? 
Have you checked the normal direction of the mesh? 
also I did find this…There are a few possible reasons why Remeshing in Blender may be damaging the arms of a model but not other parts:
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Geometry complexity: The arms may have more intricate shapes, creases, folds, etc that are more difficult for the remesh modifier to reconstruct accurately compared to smoother areas.
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Source topology: The original mesh topology in the arm areas may not have been optimized for remeshing. Poor edge flow or non-quads can cause issues.
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Self-intersections: Remeshing tries to maintain the overall volume and shape, but intricate geometries are more prone to intersecting themselves during the process.
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Preserve details setting: The arms may contain more fine details that exceed the settings for what should be preserved during remeshing.
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Non-manifold geometry: Intersecting edges or non-joined verts in the arm area could cause problems.
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Object scale: Very large or small scales relative to the original mesh resolution may not remesh well.
To fix it, some things to try are reworking the arm topology, subdividing first to simplify the geometry, decreasing the target face count, increasing preserve details, cleaning up intersections/non-manifold edges. Checking the model itself for any pre-existing issues is also worthwhile. Proper cleanup and prep of the source mesh helps ensure a clean remesh.
I tried taking down the poly count of the arms before re-meshing and it still turned black so I’m not sure that was specifically the issue. also in layout mode It displays the arms black as I have posted above but in “Sculpting” tab at the top bar…the model displays as it should. 
I see you have a multires modifier on the arms. Could it be in cause? I can imagine multires not working well with remeshing, depending on the order in which you did things.
Try deleting the modifier to see if it’s in cause.
Then, the remesh probably gave the object black vertex colors.