A lot of people out there think/are stuck with an idea that your subject has to be some thing. But that’s not true, subjects can be different. Not just some person, building, landscape, mug but think about something else. Why not color? Contrast? Emotions? Something else!
Just take this image as an example. Most colors in scene are greyish and then I saw this blue boat. Not the best image I can produce, but it makes my point 😉