I dont know why in 3d texture paint mode, my color appear many rings like in the rights.
It should appear like in 2D paint mode, color transition in same position is soft and more blended.
Does anyone know how to solve this issue?
Does the problem persist when rendered? It could be just the viewing mode you're in is displaying it like that and there isn't actually an issue when rendered.
It does not happen in render, but I feel it quite weird to switch back and fourth between modes to see if I paint color right.
That is simply an artifact of the lower color depth in the viewport , 16bit color banding you can see the same effect in lots of older video games. it does make painting less precise.
I don't think so i'm afraid. , maybe someone else might know a work around. the 3D viewports run in lower res and colour depth i imagine to keep them more responsive.
In the blender preferences there are options for viewport multi sampling and texture limits and anisotropic settings, you might get a more acceptable display if you change some of them. i cant guarantee anything i suggest you experiment with each of those settings and see if the change is favorable.
Sometimes you just gotta poke buttons to see whats what.
Try to tweak those, nothing change. Guess I will need both texture paint and uv paint windows to check color display then.