Hi Bob,
The top flag was originally white in colour but has stained "yellowish" as time goes by.
The "White over Yellow" combination of leg-flag is used for all waders leg-flagged in Hong Kong to follow the protocol agreed with all wader researchers in the Asia Pacific.
It is essential to use the combination of colour so that birdwatchers/researchers can know where the bird was ringed and flagged in the field.
You may have a look at this website:
http://www.shorebird-network.net/shorebirds/shorebird-leg-flags/
Regards,
Katherine
