The best option to add a bit of color to a rainy day would be to carry the Colour Change Umbrella.
Just as the name suggests, the Colour Change Umbrella is a hue-shifting parasol that makes gloomy days just a little brighter. The top has several graphics of raindrops, which are in white. Once the images make contact with rain water, they miraculously change into several colors. This is made possible with a special ink that's been used to print out the raindrops.
With the Colour Change Umbrella, rainy days may not be as gray or gloomy anymore. This will definitely liven up the mood with its vibrant, ever-changing abilities.