Most images/footage of flags can be sold as royalty-free content, some only as editorial content. However, certain flags are not allowed on Colourbox as neither royalty-free nor editorial content.

Not allowed on Colourbox:

The National Flag of Panama
The national flag of Panama cannot be used as neither commercial nor editorial material. The symbols of the Panamanian nation are protected both in Panama and in the countries of the Paris Union Convention (177 countries), and all marketing, promotion, information or reproduction of the system is prohibited.

The National Flag of Singapore
The national flag of Singapore cannot be used for commercial purposes without each use being cleared by the Singaporean Government.