P: New user interface lacks contrast and many usability cues, lots of other problems

Try calling Customer Support and see if they can help?

I have zero options other than CC 2015 😞

Try un-installing CS6 (doing it through the Desktop CC Panel) — but do preserve your Prefs and Settings!

Then click to Re-install a Ps Older version and you should see this "Available Versions" drop-down list after you click on the "Ps Install" button:

I have it but my only option for an older version is CS6, nothing older in CC.

That seems totally unfair!

If someone is paying for a CC subscription, they should surely have the same privileges as anyone else who is subscribing — regardless of when they joined CC?!

Check CC / Apps list to see that you really haven't got access. Half way down the list you should see this:

If you really can't find it, I would call Customer Service and ask for this to be put right.

It seems I don't have access to previous versions of CC, I'm assuming because we just got it.

For starters:
1. Put three-dimensionality back into the UI because the undifferentiated "Flat" look slows down recognizability (and thus efficiency and working-speed) enormously.

2. Make the Selection "Ants" and the Pen Tool Paths, Points and Handles MUCH more visible (stronger lines) and make them adopt complementary colours from the background image.

3. Allow the user the option of selecting colours for Layers and selected tools and fields if we want to because not everyone is distracted by the use of colour although the UX team apparently are?!

Anna:

If you have CC, look for "Previous Versions" in the Desktop Creative Cloud. Open the flippy arrow and you should see "Ps CC 2014". That version will give you the old, and much nicer, UI and is also a considerable upgrade from CS6.

I just upgraded to CC yesterday at work and after retouching two photos went back to using CS6.  The flat grey on grey is completely pointless.

The ACR panel with the sliders should be light if you set the Prefs accordingly . The "apron" area around the image can be set to any tone that you choose. Just Control-click on the apron and choose a colour from the drop-down menu.