Vertex colors can be saved as follows:
If Points Only is used, the colors between the points will be interpolated, which will always produce soft transitions. If Polygon Points is used, hard color edges will result. The respective polygons must be selected and the Paint Tool’s Selected Only option must be enabled.
If you switch between modes, the colors will be converted into each other. This is done with no problem from Points Only to Polygon Points but information will be lost the other way around since each point can only save 1 color/alpha value and multiple color values would have to be transmitted.
In addition to the RGB colors, a grayscale channel can also be saved and painted. Even though it’s named ,alpha’, it has no effect on the display of the RGB colors (but it will be evaluated when the Vertex shader is rendered in the Alpha channel). It can be applied for any purpose. If the Vertex Color tag is activated you can define here if the RGB or the Alpha channel should be displayed in the Viewport.
If this option is enabled, vertex colors will be displayed (in point form) regardless of selections or active modes. If this option is disabled, the object and tag must be selected as well as the respective component mode.