I'm banging my head to a wall here:

 1.Epson driver settings is – "Watercolor paper Radiant white" and ink type is PK as one needed.
 2.In QU 'Printers and settings' tab the media type is not recognized but shows as "Unlisted[369]"

When I'm changing in QU to the correct media type (Watercolor paper Radiant white) the INK IN THE DRIVER IS GOING BACK TO MK!

What's going on here? Any advice?
Thank you!!!

Rani,
I am using an R2400 printer driver as thatis what the paper calls for (looking in google).

I get PK ink showing when I use that paper. Sounds like that is what you wanted, right?

Where are you seeing MK black?
See snap 129 below. See mouse pointer

Fred

I want PK.
when I set the media type in QU I'm getting an error for changing to MK in the printer itself. (change ink PK to MK)
once I set (in the driver) back to PK (what I want) – in QU the media type in for Unlisted…

Epson has defined the watercolor radiant white paper as using MK ink.  You can see that in the driver: the driver does the same thing as Qimage when you select watercolor radiant white as the paper type in the driver: if you set the paper type to something else and then pick watercolor radiant white again, you'll see that the driver sets the ink back to MK as soon as you pick watercolor radiant white paper.  Presumably this is because Epson intends matte black ink to be used with that paper.

They give you the option (for that paper) to override that MK setting and choose PK instead.  When you do that, your paper type no longer conforms to the "standard" settings defined for watercolor radiant white paper so the true paper type is unlisted.  The 369 is Qimage telling you that the driver picked a paper index of 369 and index 369 has no text description.  This basically tells you that you are using a "customized" paper type that is not one of the standard selections.

Bottom line: you are creating a new/customized paper type when you change the black ink and that customized paper type can't be selected from the list of standard types.  Just change it in the driver as you've been doing and save that as a printer setup.  When you load that printer setup, the paper type will be listed as Unlisted [369] and will use the PK ink you specified.  Everything works fine; you just can't select your customized paper type from the drop-down list of standard types (because it is no longer a standard type).

P.S.  Epson has an opportunity to improve their driver here.  In the driver, you can save the PK ink setting and create a user defined paper type and name it something like "Watercolor RW - PK".  At that point, the Epson driver should assign a text description of "Watercolor RW - PK" to paper index 369 and it would show up in the drop-down list.  But they don't... so the saved paper type is still unlisted even though it shows in the driver.  An oversight by Epson in their driver.

Regards,
Mike