How to create a vector based on a pattern match using R?

In R, I have a vector containing characters:

v <- c("X412A-Y423A", "X400A-Y405B", "X499A-Y448B", "X455A-Y213A")

I want to create a vector based on this one, depending on the last character in each string (A or B), the new vector will have a different value (red or blue) such as:

vnew <- c("red","blue","blue","red")

Any help would be appreciated.