B&W + Colour Ink Question Epson 1290

I have been printing a rather large quantity of letters and documents on my Epson 1290 over a period of a few days, every print so far has been made using the black ink only as selected on the printing parameters dialog - I have noticed that the colour ink cartridge is showing the same use as the black cartridge - is this normal?

The only ink that the colour cartridge should have used is when the print heads were cleaned. Yet the black cartridge is showing about ¼ full and the colour almost exactly the same.

Can anyone comment or offer advice.

Thanks in advance

NN