This indicates the reliability of the address as a postal delivery address:

• green = The address has been verified. Letters to this address should arrive without problems.
• yellow = The address has been partially verified and corresponds to other addresses and is therefore most likely correct. Letters to this address should arrive without problems.
• red = The address is not a valid postal address. However, it may be an address you can visit, e.g. a monument, a bus stop.
• yellow flashing: The address is still being checked. Parts of the address may still change. If you have been given the address code for this delivery address, you can assume that items will arrive there.