glClearIndex - specify the clear value for the color index
buffers

glClearIndex
	glClearIndex(c) -> None

void glClearIndex( GLfloat c )

c  Specifies the index used when the color index buffers are
   cleared.  The initial value is 0.

glClearIndex specifies the index used	by glClear to clear
the color index buffers.  c is not clamped.  Rather, c is
converted to a fixed-point value with	unspecified precision
to the right of the binary point.  The integer part of this
value	is then	masked with 2m-1, where	m is the number	of
bits in a color index	stored in the frame buffer.

GL_INVALID_OPERATION is generated if glClearIndex is
executed between the execution of glBegin and	the
corresponding	execution of glEnd.

glGet	with argument GL_INDEX_CLEAR_VALUE
glGet	with argument GL_INDEX_BITS

glClear