Carelogger is a tool for diabetics that tracks different diabetes health metrics. The personal logbooks for patients are free. Business accounts allow doctors to monitor sereral patients and are paid. The company wanted to increase the number of signups for their tool on their homepage.
Choosing a signup button color that stands out more (red) will increase signups
There are two possible explanations; the red color in it self is more appealing to customers or the red color is effective because of the contrast with other design elements on the page.