Pass a value to the backend from custom options (dropdown) programatically

Pass a value to the backend from custom options (dropdown) programatically

I've got this problem that I can't solve. Partly because I can't explain
it with the right terms. I'm new to this so sorry for this clumsy
question.
Below you can see an overview of my goal.
In my product i have a dropdown custom option.
For Example: I have Color ,in that i have Red, White, Black
I want to set Set White is Default value Programatically.
I am using Magento CE1.7.0.2
Any Ideas ?