Canon iR C6800 Series Service Manual page 305

If a color developing cylinder was allowed to remain in contact with the sensitive drum at time of black development,
the cylinder would disturb the black toner image. To prevent such disturbance, the machine moves the developing
rotary to its home position so that a color developing cylinder will never be opposite the photosensitive drum.
The following shows the position of Y toner cartridge access and point of M development.
Flag
<Point of Y Toner Cartridge Access>
F-7-34
PS8
PS8
<Point of M Development>
Flag
Chapter 7
7-39