AT&T 6300 Programmer's Manual page 204

COLOR
Statement
7-48
Text Mode
To make characters blink for a specific color,
you should set "foreground" equal to 16 plus
the color number.
You may select only colors 0 through 7 for
"background.' ,
In a monochrome system the following values
can be used for "foreground":
• 0 Black
• 1 Underlined character with white foreground
• 2-7 White
Adding 8 to the number of the desired color
gives you the color in high-intensity.
You can make the character blink by adding
16 to the number of the desired color.
For "background" you may select the
following values:
0-6 Black
7 White