From United,
"April is National Arab American Heritage Month. The balloons were a part of our Arab American Heritage Month celebration, which we held had at the gate of our Dubai flight on April 30.
The intention was to have the balloon colors match the United Arab Emirates flag, and many Arab countries have similar color schemes on their flags.
We do celebrations like these for many heritages/ethnicities during a designated period in which they’re celebrated more broadly (i.e. a heritage month)."