I need to check out your main site more often, you put up some interesting stuff. I didn't read it carefully enough to get a complete mental picture, and I didn't really picture the umbrella, just a guys legs running in the rain. Emily said that the umbrella was black. Emily says that she visualizes just about everything.
Poincare had to visualize his lectures that he listened to because his eyesight was so bad. Euler was able to visualize everything even after he went blind. In fact I can't think of a single great mathematician that couldn't visualize. You're going to be the first one.
I think that your mind just attaches whatever is simple to the details that your not focusing on. Since the focus of the story seems to be Bob, his ever increasing pace and the rain, that's what I focused on. I could "see" the quickening rain and Bob increasing his pace. In my mind, I didn't really see anything more than his lower body up to about his thighs and the rain drops hitting the ground. So, when he pulled out the umbrella, it was black. The story hadn't pulled my mind into that direction. An example of what I mean is that if story has started to talk what kind of umbrella he had before he opened it, then I would have "seen" that instead.
Maybe he is getting it out of his trunk to use later. But more likely is that he drives an extreme stretch limo, and his door is at least a quarter mile from his trunk.
I pictured the umbrella black, because presumably Bob is a dude. And no self-respecting businessman with a tan trenchcoat would buy a brightly colored umbrella.
I have also come to the conclusion that Bob is an idiot. First of all, he strolled out to his car. Who strolls nowadays? Second, who would open the trunk in a downpour to get out an umbrella, just for those last few seconds before you get in the car? This does not make sense! Chewbacca is a Wookie!