Final answer:
The common color for an icon indicating availability to join a video visit in an appointment list is typically green, adhering to general UI/UX design practices.
Step-by-step explanation:
The color that the video visit icon becomes in a list of appointments on an account's "Appointments" tab when a member is able to join is typically designed to be intuitive and indicate the status clearly. Although the actual color can vary depending on the specific application or platform design, green is a common color used to signify that an action, such as joining a video visit, is available or that the status is 'go'. In this context, if the platform follows these common conventions, the answer would likely be (b) Green. However, without specific information about the platform in question, this is based on general UI/UX design practices.