We see these beauties around here only when the air is heavy with moisture, as it was today. They have grossed me out from the first time I set eyes on one. Out of curiosity, I googled banana slug, and learned that some really are yellow, like the fruit. All the banana slugs I have ever seen look like the one pictured. In fact, this one is not even particularly large. To give an idea of scale, the brick it is climbing is just over 4 inches high (about 11 cm).
On a side note, Eugene, Oregon is my nearest city, and they have a slug queen who came from the weirdness of the populace. It is entertaining to read about, and I will vouch that this has been going on for many years!