Question Why is white not white in Screen Space Camera UI?

Consider the following example scene where there is no light, no Volume or else. The only object is twice the exact same canvas with a white (255,255,255) image covering half of the screen, one time set to Screen Space Overlay, the other time to Screen Space camera.

Why is the screen space camera UI rendering in a grayish tone and how can I fix that?

 

What component is the image?
Could you send a screenshot of the gameobject and the issue you have?

 

Oh, sorry, I wanted to attach images and totally forgot about that

I edited the original post

 

Update: it has to do with the Volume Mask settings of the camera component. If I exclude the default layer from the Volume Mask, then it renders correctly, but why is the color affected by these settings?

 

Because screen space puts the UI inside of the camera rendering loop

 

Yes, but there is nothing active in the scene that should affect the UI if you look at the top image. What am I missing?

 

Still affected by post processing especially tonemapping iirc

 

can you elaborate on that? Where is the tonemapping happening? There is no volume in the scene that would control that

EDIT: Found it in the HDRP global settings. Finally! Thank you!