Oki LD670 User Manual page 103

Then, press and hold down the FEED switch for one second or longer to
accept the selection.
The printer prints the following when you accept the selection of "PRINT
COLOR":
7. Select "2 COLOR" as your option.
Press the FEED switch briefly (one second or less) once to move to
"2 COLOR".
Mono
2 Color
Mono
Selection Item
Print Color
2 Color
↑
Mono
2 Color
Mono
Selection Item
101