P.,
I don't mean to laugh, but this is exactly what my children are pulling on me lately. It makes me chuckle a bit and I'll share a story my Mother In Law shared with me.
My dear sweet patient husband who I love without limits tried the same thing with her. Two and a half years old, in a high chair and the battle was 'white milk, chocolate milk'. Now, my wonderful mother in law - who I call Mom, she's so great - went patiently back and forth, back and forth bringing the two different cups to the high chair. Finally, she dumped the cup on his head. We tease my husband about it to this day.
Now, I am not suggesting anything so drastic, but this amazingly patient and loving woman went through the same problems you and I are having and handled it with no further arguements from her son.
Let your son know you're not a waiter, short-order cook, butler and have him stand by his choice. No arguements. No anger. No emotion. Just 'that's that', you made your choice. Walk away if you have to.
I have started taking away the options. No more "do you kids want water or milk, I just bring what I bring and that's it. If they don't like it, I calmly take the drink away. No more "do you want to wear the blue shirt or the red shirt" I just bring them what they're wearing. And that's that.
When they can start making choices again without the yo yo effect, I will open the door up a bit on their choices.
And if all else fails, dump milk on his head.
Good luck,
J.