Just an update on this, though no one has replied.
A bit more experimentation shows that it is not just actually that render pink, it is anything white. The skies in the shots I experiemted with were white, which is what made me think it was skies that were the problem (somehow). Since then, I have tried importing shots to NIK colour-handling plug-ins that have blue skies and clouds. The skies stay blue, but the clouds render pink.
The same goes for cityscales (say) with white buildings - they render pink too.
The issue I have therefore seems to be the NIK plugins interpreting white sent from Aperture as pink.
"Aperture➞Preferences➞Export➞External Editor Color Space"?
Also, note that pink is a tint of a hue, as is "white". The difference is that the luminance of things described as "white" is high enough that we don't or can't identify the hue. What hue are the white clouds and buildings that show as pink in Nik?
*Slaps self hard around the head*
Why did I not think of looking there?
You are right, of course. That's where the issue lay. When I upgraded to Aperture 3.3, the upgrade clearly over-wrote the Adobe Color Space I had previously specified, and substituted the color space for my Canon printer in the "export" field. Changing it has completely solved the problem as far as I can see.
I had not expected the upgrade to overwrite user preferences. I wonder whether the fact that it appears to do so in some cases will answer problems others are having. Hasn't solved my issues with Photostream, however. Even with all the preferences off, Aperture is busy exporting away!
Very many thanks, Kirby.
Glad to help. Don't hurt yourself .
I had not expected the upgrade to overwrite user preferences. I wonder whether the fact that it appears to do so in some cases will answer problems others are having.
Imho, upgrades *must* inform users of changes made to user prefs. Somewhere in my notes about Ap3.3 is another pref that was changed. *Looks at a terminal morraine of Post-Its, index cards, detached Moleskine pages, paper towels (some written on), eye-glass wipes, out-dated PDF print-outs, and chocolate bar wrappers ... * Don't recall which one it was, though.