8715 using color to make black

[B_Will]

Is the 8715 using color to make black because the black cartridge is low?

My 8715 color setup cartridges were empty and I replaced them.

The black setup cartridge is showing as low so I did not replace it.

The black level has not changed even though I print mostly in black.

All the color cartridges show as being used by the same amount.

[Valsimot]

Some small amount of colour ink cartridges is used to mix with black ink cartridge when printing black, also all 4 ink cartridges are used for maintaining printhead during printer turning ON, and printhead cleaning.

If you are printing only black ( or in most cases black)  then you should replace black setup cartridge first, later colour ones. It's strange that your setup black still contains ink, and you had to already replace setup colours.

Any chance that someone is printing in a colour that you don't know? 

[B_Will]

I am the sole user of the printer.

[Valsimot]

The strange thing is regarding your black ink cartridge status is shoving Previously Used Genuine HP Cartridge Installed

Is this your first setup black that came with the printer or not, what is your current total page count black/colour?

[B_Will]

The black cartridge is the setup cartridge that came with the printer.

Total page count is 538.

[Valsimot]

There is no other reasonable explanation, except that you ( or someone) are printing in colour too, not only in black.

The setup black can print 750 pages at 5% coverage, setup colour can print 400 pages at 5% coverage, you printed 538.