INT 10 - VIDEO - UltraVision v1.2+ - SET UNDERLINE STATUS (EGA,VGA)
AX = CD07h
CL = hardware underline status
00h off (color systems only)
01h underline below characters
02h strike through characters
BL = foreground color for normal text (FFh = current)
BH = foreground color for bright text (FFh = current)
Return: CL = hardware underline status
BL = current foreground color for normal text
BH = current foreground color for bright text
Notes:  when underline or strikeout is enabled in color text modes, the
specified colors will be assigned temporarily to colors 01h and 09h,
allowing affected text to match non-underlined text.  The color
remapping uses values from the current onscreen palette regardless
of the palette locking status (see AX=CD01h)
specify the standard colors (BL=01h,BH=09h) to enable underline or
strikeout without color remapping

See also: 10CD08

10CD07 - VIDEO - UltraVision v1.2+ - SET UNDERLINE STATUS (EGA,VGA)