I have made a mesh and some of the meshes have this weird, black shading. I have tried shading flat, autosmooth, recalculating normals- but nothing works. I try to recolour the mesh in studio and it just leaves a washed-out darkened version of it.
Are you sure normals are facing the right direction inside Blender?
Try messing with the Weighted Normal modifier.
(If faces turn red, then you are cooked.) Just press Shift+N.
I think it worked- thank you 
As @Yarik_superpro said, make sure your Normals are facing the right way.
Also,
Select all faces, go to the Mesh tool, go to Normals, and select ‘reset vectors’. If you’ve moved vertices around it can make some strange directions for vertices, edges, and faces so this tool resets everything.
It also helps if you’ve had to flip some normals.
If the faces still look oddly shaded try the same menu above, but click smooth vectors, then click reset vectors. It’s worked for me before. They occasionally give weird edges even though all of them are joined normally. It may happen if you’ve started making faces from one face with normals facing one direction, and joined them to a face with completely different normals.
Another thing may be if you’ve got extra vertices at the same spot. One face may be joined to one vertex the next face may be joined to the second vertex, which gives an odd sharp edge in adjoining faces.
Select all the vertices in the area you’re concerned with. Go to the Mesh menu > Clean up > Merge by distance. If the vertices are within about .001 m they’ll join. There’s a popup at the bottom left of the screen where you can change that value to something higher if you want.
