If you're looking for a project that you can shoot over several weeks or even months have a go at creating a collection of images that all share the same colour.
As this is something that can take quite some time to do, it's something you can shoot alongside your other types of photography or you could try working on several different 'colour themes' all at once.
Your subjects don't have to be the same but it's important that the colour is, that way once you have a few images in your collection, you can begin to group them together to create panels and triptychs to hang on walls or post in online galleries.
As you don't know what you'll be photographing until you see it, it's best to take a zoom lens out with you. By doing so you'll have various focal lengths to play with plus if you plan on walking for a while, you won't have lots of kit weighing you down.
You can sit and create a list of items organised into colour groups you can photograph or try visiting a location and wandering around to see which colour would be best to shoot in that particular place.
Do remember that the lack of other colours does mean you'll have to work harder to ensure your composition is interesting. That means you need to pay particular attention to textures, lines, shapes and framing.