My output is washed out when in windowed

I have the following setup:

RGBA8_Unorm_srgb swapchain buffer
RGBA16Float render targets
RGBA8_Unorm_srgb color textures
RGBA8_Unorm tangent normals textures

I use the render targets for actual rendering. In the very last step in my pipeline, I use the render target as a shader resource and do a fullscreen post processing via shader onto the swapchain buffer as render target

However, I noticed that when I am in fullscreen, I have darker (desired) output compared to when I am in windowed. In Windowed, everything looks washed out and brighter.

Windowed

Fullscreen

What is the cause of this?