Color of the last ball II

You have 20 blue balls and 13 red balls in a bag.
You put your hand in and remove two at a time.

• If they’re of the same color, you add a blue ball to the bag.
• If they’re of different colors, you add a red ball to the bag.

Assume you have an enormous supply of blue & red balls for this purpose.

Note: When you take the two balls out, you don’t put them back in, so the number of balls in the bag keeps decreasing.

What will be the color of the last ball left in the bag?