There are three red, white and black glass balls in the box. How many balls can you feel from the box to ensure that you can touch the same color balls?

There are three red, white and black glass balls in the box. How many balls can you feel from the box to ensure that you can touch the same color balls?

Find out three, maybe one in red, one in white and one in black
Now as long as you touch one more, there must be a ball of the same color
So at least we need to figure out: 3 + 1 = 4