Default sRGB color profile

> The document has no color profile, but photoshop has to use SOMETHING to display your
>documents -- and it defaults to using the default RGB profile from color settings.

Which is exactly the probelm I ran into. For unmanaged images the filterRecord->iCCprofileData field is NULL and I currently just fall back to the srgb profile. Is there a way for a plugin to determine what the default RGB profile PS is using?

Just want to add this, because there is a lot of misunderstanding about this:

The working space profile is not directly used for onscreen display.
Working space is the colorspace where image processing calculations are done.
When the image is displayed, then it is converted from working space profile into the monitor's profile which is taken from window's colormanagement preferences. Then it is copied to the display buffer and is displayed.

So photoshop needs to have some (eventually default) profile to convert into monitor colorspace for display.

The document has no color profile, but photoshop has to use SOMETHING to display your documents -- and it defaults to using the default RGB profile from color settings.

No. Not exactly.

If the image has a colorspace then it is ignored.
The (default) workingspace that is selected from the Color Settings dialog is used.