Hi, thanks for playing the game! I'll admit that it was my first time working on a puzzle game, and I didn't get a chance to play test it (which always ends well), which would have warned me that I needed to include a tutorial. Based on others comments as well it was not clear which fireflies the player needed to pay attention to in order to solve the puzzle, which is on me. The idea is the firefly on the left is signaling to the firefly on the right who will turn on the floodlight if you get the answer right, so don't pay attention to them and only focus on the colored fireflies.
But in answer to your question, the answer to the first level is red! If you ever get to the fifth level, I also realized that there are some mixed up fireflies, the red->green firefly should be blue->green, and the blue->yellow firefly should be red->yellow.
-Ramble