Learn English – the difference between I’ll and I will

You would not say that you merge the colors.

You also would not say that you mix into traffic.

I am not actually sure why, a quick dictionary search didn't make it clearer.

But I think you merge things when they keep their general form or configuration but blend together... where as you mix things when they get all out of order in the process.

Like with a deck of cards - merging two halves of the decks (shuffling -- we never actually say 'merge' about cards) -- mixing would be like dumping all the cards on the table and spreading them around with your hands.

Merge is less commonly used, btw - The two rivers merged into one, We merged the two businesses, there was an accident where the express lane merges into traffic.

Both express possession, of course.

We use 's with singular nouns. For example, "my son's toys" will be "the toys that belong to my son".

We use only an apostrophe (') after plural nouns that end in -s: "my sons' toys" means that I have more than one son and these are their toys.

We use 's for possession with the other plural nouns. For example: "my children's toys; women's wishes, etc.