glColorMask -	enable and disable writing of frame buffer
color	components

glColorMask
	glColorMask(red, gree, blue, alpha) -> None

void glColorMask( GLboolean red,
                  GLboolean green,
                  GLboolean blue,
                  GLboolean alpha )

red, green, blue, alpha
                      Specify	whether	red, green, blue, and
                      alpha can or cannot be written into
                      the frame buffer.  The initial values
                      are all	GL_TRUE, indicating that the
                      color components can be	written.

glColorMask specifies	whether	the individual color
components in	the frame buffer can or	cannot be written.  If
red is GL_FALSE, for example,	no change is made to the red
component of any pixel in any	of the color buffers,
regardless of	the drawing operation attempted.

Changes to individual	bits of	components cannot be
controlled.  Rather, changes are either enabled or disabled
for entire color components.

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

glGet	with argument GL_COLOR_WRITEMASK
glGet	with argument GL_RGBA_MODE

glColor, glColorPointer, glDepthMask,	glIndex,
glIndexPointer, glIndexMask, glStencilMask