Oki PT390 Manuel D'utilisation page 83

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
"CUSTOMIZE VALUE":
6. Select "PRINT COLOR" as your option.
Press the FEED switch briefly (one second or less) three times to move to
"PRINT COLOR."
USER NV MEMORY
RETURN TO SETUP MENU
RETURN TO UP
LOW POWER
MAX SPEED
BK DENSITY (2COLER)
PRINT DENSITY
PRINT COLOR
PRINT WIDTH
NV GRAPHIC MENORY
USER NV MEMORY
SELECTION ITEM
PRINT COLOR
↑
PRINT WIDTH
↑
NV GRAPHIC MENORY
↑
USER NV MEMORY
RETURN TO SETUP MENU
RETURN TO UP
LOW POWER
MAX SPEED
BK DENSITY (2COLER)
PRINT DENSITY
PRINT COLOR
PRINT WIDTH
NV GRAPHIC MENORY
USER NV MEMORY
SELECTION ITEM
81