Light Gray Balloons are called Silver Balloons

"Silver" is used in various places in the game data rather than "light gray". I am not sure this is a bug.

Thank you for your report!
However, this issue has been closed as Invalid.

This is more of a feature request or a suggestion than a bug with the game.

We're very keen to hear your ideas though, so please head over to the Minecraft Feedback Site where you can search and vote for existing topics, or add a new thread if necessary.

Quick Links:
📓 Issue Guidelines – 💬 Mojang Support – 📧 Suggestions – 📖 Minecraft Wiki