There's reduced mandarin juice in the white chocolate ganache, and mandarin zest in the shell.
And I found out the secret of getting the really bright colours.
You use a lot of food colouring. Who knew? This is half a teaspoon or so of orange Wiltons gel food colouring.
And the way to stop the cracking was to turn the oven DOWN. I was using 140 (fan forced) and I dropped it to 120 degrees. I also popped a thermometer into the oven, to see what temperature it was REALLY at. Turns out that 120 on the dial, and fan forced, gives us 140 in the oven. And I baked only one tray at a time (there were 7 trays!). Watched Flash Gordon while I shuffled trays.
Now the issue is the big air pocket under the perfect top of the shell. Look at that top macaron in the stack - some of them you can see right through! So that's not perfect. We're in the right ballpark though.