Hi,
Thanks for capturing the video and sharing it with us.
As mentioned above, it turned out that there is a bug where the incorrect color space was being assigned to the bitmap when the file is dragged and dropped. So please avoid d&d until we fix it.
Once the correct color space (sRGB in this case) is assigned to the bitmap, the only difference you'll get compared to an image viewing application will be the tone-mapping (aka. view transform) applied to the rendered scene image output. By default, the "ACES 1.0 SDR-video" view transform is applied to the render results (including the viewport rendering). Among other things this does a dynamic range compression to display high dynamic render result image in low dynamic range monitor, bringing details in the highlight etc. This will also change the mid-tones to open-up a room for the highlights, so probably the difference you're seeing is this one.
In your particular case, you're interested in replicating the texture space tones, not the rendering result, thus you're removing the lighting effects by picking flat shading. You also need to remove the tone-mapping:
you can do that in the active viewport settings dialog, color management tab by selecting un-tone-mapped as the view transform for that viewport. Alternatively, you can change the default value that the viewports will use in the system color management settings.
Let us if this works for you.
Cuneyt Ozdas
Principle Software Engineer