What You Did
You compared the heat-absorbing properties of different colored paper.
The water in the jar with the black paper should be warmer than the one with white paper.
My first run of this experiment was a dud. I chose a time too late in the afternoon, around 3pm, and when I checked them, after only one hour, the water was the same temperature in both cups. I also used plastic cups instead of glass ones, which don’t conduct heat nearly as well.The results can be skewed if your glasses or jars are not identical in size and filled with the same amount of water.
Vary the time of day when you start the experiment. Vary the amount of time you leave the glasses in the sunlight. Repeat the experiment in the shade or in a closet completely away from a light source. Try using artificial lighting, like traditional tungsten bulbs or fluorescent lighting. You can compare different artificial light sources, or vary the distance between light source and the cups.Try different colors of paper, or different colors of drinking glasses