Can't paint or select bones in weight paint mode I just started using Blender and started a little project. I made a model and the bones myself. I used the automatic weight when parenting the armature and the model.
When I moved the legs in pose mode, the middle body bent so I thought I will just go weight painting and make some adjustments. But the model is mostly grey in weight paint mode. The bones are grey also when selected. Just a tiny bit of color is visible near the selected bone.

I tested with a cube and it worked well. I have been trying to find a similar case from the internet but have not seen one. Thank you for the help.
You have the Face Mask activated. It's a mode that allows you to only paint on whatever faces have already been selected when you were last in Edit Mode. It's activated by the button near the red arrow shown here. Click it again to return to the more deeply colored standard weight paint mode.