One color doesn't print

Forgive me if this has been addressed in another thread.  I'm using an AIO 964 printer, USB connection, and I have a Series 5 color cartridge that displays an 80% full ink level.  The red ink is not printing.  I have used the Clean Cartridges utility on the printer several times, and I used the Ink Cartridge Maintenance instructions in the owner's manual to clean the ink slots with a damp cloth and the contacts on the cartridge and in the printer with a dry cloth.  Red ink comes out of the bottom of the cartridge but does not print.  Blue and yellow are printing very well.

I purchased two of these color cartridges from Dell 2 years ago.  The first one worked well, and I put this one in only recently (I do very little color printing).  I'm prepared to accept that the red may just be gone, even though red ink still physically comes out of the bottom of the cartridge.  To be honest, I can't remember if this cartridge ever printed out red, that's how little color printing I do.

Here are my questions:

1. Doesn't the ink level of the color cartridge display as low as the lowest color in the cartridge?

2. Is it possible to find out the levels of the individual colors in a color cartridge? 

3. How can I distinguish between the red having run out and there being a sensor defect on this cartridge?

Thanks in advance for any help.