Earlier this year, when I had some extra spare time, I made some colour-themed collages in Photoshop with some of my old photos. Here is the "red" collage:
The collages were easy to make: All I did was search for the photos that I wanted to use in them, crop down the photos to include just the part that I wanted as well as make them all the same size and shape. Then I copied and pasted the photos into a new Photoshop document and arranged them in a pleasing pattern to create the resulting collage. I made ten collages in total, each one for a different colour.
About a year ago, I made a similar series of collages using scissors, glue, and paper in my art journal. Here is the "blue" collage:
These sorts of collages, whether made of paper or pixels, are fun to make, whether you want to relax on a hot afternoon (the blue one would be especially good for that!), explore colour, or use up some extra paper collage materials.