The Blue dongle has a 1090 Mhz filter builtin, and will perform poor for 978 Mhz, but good for 1090 Mhz. Use Blue dongle for 1090 Mhz by serializing it with 8-digit serial number 00001090.
The Orange dongle has no builtin filter and will work good for both 1090 Mhz and 978 Mhz. Use Orange dongle for 978 Mhz by serializing it with 8-digit serial number 00000978.
NOTE:
Do not plug both dongles simultaneously to RPi when serializing. Plug only one dongle in RPi and serialize it. Put a sticker on it and write the serial number with which you have serialized it.
After serializing first dongle, unplug it and plug the other dongle and serialize it. Put a sticker on it and write the serial number with which you have serialized it.
After serialization, dongles are required to be unplugged, then replugged in RPi and RPi rebooted to pick the serial numbers.
If later you want to check serial number of the dongles, do this:
(1) Install package rtl-sdr
sudo apt install rtl-sdr
(2) Keeping plugged only one dongle, give following commands. The last command will display dongle’s serial number
sudo systemctl stop piaware dump1090-fa dump978-fa
rtl_test -t
(3) Unplug first dongle and plugin second dongle and again give above two commands to display second dongle’s serial number.
(4) Plug-in both dongles
(5) Reboot RPi