I can't paint the whole model in texture paint mode I have a problem in texture paint mode. If I unwrap the model, I can't paint the entire mesh. It remains entirely white. More details in this picture.



If you can answer too why is it stay black :/ but the properly uv texture changing transparent white.
If it stays 'full white' then quite possible you don't have an image texture assigned to the UVs yet - in the Tool Bar, check for a warning to 'add paint slot below' as in the attached picture.