Epson SureColor P600 Color Ink Consumption

[BirdWife]

I have a Epson SureColor P600 printer that I ONLY use to print gray scale. The all cartridges that are currently in it are the originals that I put in when I received this printer in January 2019. The three black cartridges (I dont use the glossy black), are going down in amounts that I would expect, however the colour ink is also going down, all at varying amounts. I understand that every time the printer is turned on and it prints a "small amount" of colour ink is used to clear the print heads so that they dont clog. What I do not understand is why some of the colour ink is being consumed at the same rate as my black ink, while other coloured ink is barely being used. Using Epson's logic, all colour ink should be being consumed at the same rate if it is only being used to clear the printer heads.

I called Epson to ask them about this and they gave me some excuse saying that the colour ink is being consumed in this manner because I am using the smaller volume cartridges that my printer came with. Once I switch to full size cartridges this will no longer happen and the colour ink will be consumed at a consistent rate across all 5 cartridges if I continue to only print gray scale.

To me this makes little to no sense - why would the volume (size) of the cartridge affect how the ink is being consumed? I have attached a picture for reference.

Is Epson correct and I am out to lunch?

 

[Shadowman]

From the literature I've read, printers use black and gray inks but also use some yellow, light magenta, and light cyan. page 225 of "Fine Art Printing for Photographers", Steinmueller and Gulbins.

 

[BirdWife]

Thank you for the replies! This makes total sense to me. I wish that the Epson representative I was speaking to would have just told me this in the first place...