FWIW the loss of detail for dark colors is unfortunately unavoidable. Don’t have time to explain this in detail atm, but it’s a side effect of the tone-mapping curve that looks more or less like this:
The dark colors (in the bottom) “flatten out”.
We tried to make a tonemapping curve that mostly removes this, but this makes it very hard to preserve hue/brightness for the medium range or compress the highlights (where colors are so bright you can’t represent them on a monitor). The current curve we’ve shipped is trying to preserve hue mid-range and compress highlights well, and dark colors had to suffer a bit.
This is the unfortunate side-effect of the whole “we need HDR and HDR requires a tone-mapper” sequence of decisions I’ve explained in Compatibility thread.
In the future we’re going to provide controls over the tonemapping curve that will allow you to affect the toe/shoulder areas explicitly, which will mean that you can effectively tune the “film” response however you like it for your game.