I don't get with your comparing between:
"ນາງ+surname" & "ແດງ+surname"
ແດງ originally means: "red"
"ນາງ" can use as calling "girl" .
The most important thing that you have to consider before you call them is, they should be younger than you.
If they are seem older than you:(Base on their ages & suppose that you are 20 years old)
less than 20 years old: ນາງ
20-30 : ນາງ, ສາວ, ເອື້ອຍ
30-50: ນ້າສາວ
50 up: ແມ່, ປ້າ
hope that it could help you