Be aware of color-blind issues. Use new black markers for the safest option. It may be difficult for color-blind people to see red, green, blue, and yellow. Be aware that color-blind and low vision users have individual variations and different preferences re: colors and background. Use strong contrast to the background, so black ink on white background may be the safest option.
Whiteboard—Challenge of a professor using a whiteboard in the room
Use a laser or a stick pointer to help focus attention on slides
Both PowerPoint and Google slides have captioning features