Why do european cars have yellowish-orange winkers ...

I believe that american cas used to have that kind of orange lights....

But about european cars I can tell you why it is orange, in our "circulation rules" orange is the color for "careful" and red is the color for "obligation/forbidden" when you turn left or right you are informing the others that you are doing that so the lights are orange, it means "be careful I'm turning left" but when you use your breaks it's to say to the car behind you "STOOOOOP"

hope this was helpful... 

"circulation rules"? what's that?

It's a good question. I found an exlanation in

I believe that it has to do with European vs. American car and safty regulations.

(BTW, I think you mean the Blinkers and not winkers ;-) )

Amber rear turn signals are required in the European Type Approval requirements for all vehicles sold or registered in the EC. In the States there is no absolute convention on the colour of rear turn signal lights. They can be either red or amber.

At American Car Imports in London http://www.americancarimports.com/technical.asp?page=tech_sva.asp where we carry out light conversions to all American cars we import into the UK, we ensure that a very neat and clever solution is achieved to comply with the law but not undermining the appearance of the vehicle.

Sorry to not be directly answering your question, but I'd just like to comment that from experience I think having the blinker lights exactly the same color as the brake lights are confusing and it's better to differentiate their colors...