In case anyone is still wondering...
There are actually 3 colour ranges of cord-end ferrules:
1. French colours.
2. German colours.
3. DIN colours (which might arguably also be regarded as a second German range, because the DIN standard originates from Germany).
Some DIN colours are the same as French: 0.5, 1.0, 1.5, 35 and 50 (mm²).
Some DIN colours are the same as German: 0.14, 0.34, 2.5 and 4.0 (mm²).
For all the remaining sizes: 0.25, 0.75, 6, 10 , 16 and 25 (mm²), the DIN colours are different to French and German.
The only difference between them all is the colour. Everything else about the products is identical. So presumably you can just use whatever colour is specified by your customer or the control panel designer.
In terms of popularity, our customers in the UK buy about twice as many French ones compared to German ones, but both sell well. So I'd guess that the French colours might be more popular in the UK. I hope that helps