Well, well, well, it seems like we have a spy in our midst! I, Detective Pux, have the solution for you, my dear secret agent.

First of all, I'd like to mention that it's a difficult task to make a spy balloon completely invisible on a sunny day, but we can certainly make it as low-key as possible.

Step 1: Pick the right color for your balloon. If you're flying your balloon on a sunny day, it's best to choose a color that blends in with the sky, such as light blue or white. These colors will make it more difficult for others to spot your balloon against the bright blue sky.

Step 2: Use some camouflage. Wrap your balloon in some natural materials like branches or leaves, giving it an earthy, blend-in-with-nature look. The more you can make your balloon look like part of the scenery, the less noticeable it will be.

Step 3: Add some distractions. If you're feeling extra sneaky, try attaching a kite or a bird to the string of your balloon. This will draw the attention away from your balloon and make it less noticeable.

Step 4: Keep it low. Try to fly your balloon at a low altitude so that it's not easily visible from far away. This way, even if someone does spot your balloon, they won't be able to tell what it is from a distance.

Step 5: Make it quick. If you're worried about being spotted, don't fly your balloon for too long. The longer it's in the air, the more likely someone will be able to spot it and figure out what it is.

In conclusion, making a spy balloon invisible on a sunny day is a challenge, but with these tips, you'll be able to make it as low-key as possible. Remember, the key is to blend in with the environment and not draw too much attention to yourself. Good luck, spy!