The actual rendered png shows nothing at this pixel(white circle), because alpha is 0.
But Render result window still has some color visible(white circle).You can see its alpha value as well in this picture above which indicate this pixel should be total transparent.
My color management setting are basically SRGB and Standard.
Is there a way making render result showing exact the same thing png does?
Alpha channel is used differently in different types of software. Then you save this image in PNG, alpha will be converted from premultiplied to straight and this pixel will be transparent. It is an actual headache for newcomers, these are just a couple of questions:
Glare Transparency Correct in Render, but lost in save to PNG
Why are transparent colours desaturated when exported?
How do I get the Glare node to output transparent instead of Black background
Glow effect invisible on transparent background
Method where RGBA channels are stored as (R, G, B, A) channels, with the RGB channels unaffected by the alpha channel. This is the alpha type used by paint programs such as Photoshop or Gimp, and used in common file formats like PNG, BMP or Targa. So, image textures or output for the web are usually straight alpha.
Method where RGBA channels are stored as (R × A, G × A, B × A, A), with the alpha multiplied into the RGB channel.
This is the natural output of render engines, with the RGB channels representing the amount of light that comes toward the viewer, and alpha representing how much of the light from the background is blocked. The OpenEXR file format uses this alpha type. So, intermediate files for rendering and compositing are often stored as premultiplied alpha.
