Why does a CMYK printer have RGB ink tanks

[PGordini]

We are having trouble printing nice tomatoe red and bright blue colors using the SG1 paper profile on our 9500MII printer.

Over the years we have noticed that the RGB ink tanks last forever, we buy the ink sets and eventually end up selling the RGB ink tanks on e-bay.We print mostly photos and occasionally web pages 

[Karl1]

Hi PGordini,

The red and green inks are enhancement inks only used slightly to make the reds and greens in colors more vibrant.  Since they are only used as enhancements, they are not used nearly as much as the other cyan, magenta and yellow colors.  So we might be able to help figure out what's happening with your colors, please answer the following:

1.  What is the source of the original image?  Is the image from a digital camera, scanner photo, web page, or other source?  What is the file size of the image?

2.  Will the image print correctly on plain paper?  I understand the picture will not look as good on plain paper, but what I am looking to determine here is if the same color issues apepar.

3.  What program was used to print the image?

4.  Are you able to print the following sample image correctly?

http://consumer.usa.canon.com/app/images/d_camera/s70_sample2.jpg

6.  Does the Nozzle Check print correctly?  Follow these steps to print a Nozzle Check from the printer:

     a.  Make sure the printer is powered on and paper is loaded into the sheet feeder.

     b.  Press and hold the RESUME button on the top of the printer until the POWER light flashes twice.

[PGordini]

The image was captured in RAW format using a 5D MKIII and processed in Lightroom 4 and then printed on a Pixma 9500 MKII using Hanemuele Photo Rag Duo. We have since found out that this paper has a small gamut due to its absorbent nature. We are trying some Semi Gloss canon paper

[Devin]

Hi PGordini,

How did your Semi-Gloss paper work for you?  Also, I wanted to let you know that since this is a pigment based ink printer, it may not print correctly on semi-gloss or glossy papers.  This printer is meant to use non-glossy papers like Matte Photo Paper which may give you a better result.  Also, processing in Lightroom can cause the photo to print incorrectly so this is why we recommend printing the sample image we provided to ensure that the issue is not the image.  Finally, the Nozzle Check confirms that the inks are ejecting correctly so please ensure that your Nozzle Check is printing correctly.

I hope this helps.