The probability of pulling out a red or blue marble can be found by adding the probability of pulling out a red marble to the probability of pulling out a blue marble.
The probability of pulling out a red marble is 6/13, since there are 6 red marbles out of a total of 13 marbles in the bag.
The probability of pulling out a blue marble is 4/13, since there are 4 blue marbles out of a total of 13 marbles in the bag.
Therefore, the probability of pulling out a red or blue marble is (6/13) + (4/13) = 10/13.
So, P(red OR blue) = 10/13.