We add a standard gradient that gets darker at the bottom of the Cover Photo on each race website. The purpose of this is to make sure the calls to action (SignUp and Donate) really stand out. This is the same method that Facebook uses on every cover photo for people or pages.
We have added an Advanced Option at the bottom of the Race Theme setup page to turn off the gradient. Please be careful using this because if you do not have the right photo it can look pretty unprofessional. Here is the setup option: