In the top navigation click on the Actions link, then on the next page click the 'New Action' button.

In the pop-up, name your action Umbrella Project (or whatever you want to call it), and describe what your action will do. In this case 'If it's raining, turn NeoPixels blue'

Here is how you will want to set up your action. Set it up to trigger the action every 5 minutes. Then if there is rain coming in the next hour, turn the NeoPixels a light blue color, and if it is actively raining, turn the NeoPixels a dark blue color. If there is no rain incoming, turn off the NeoPixels.

Once you have your new Adafruit IO Action set up like above, click the Save and Run button.