Color test swatch??

Does anyone have a color test swatch or specific CMYK settings that will allow me to print using only (or at least mostly) with a specific ink color on an HP designjet? I'm trying to isolate an issue with two of my inks (light gray, light magenta) that seem to rub off on a couple different substrates. The only way I can isolate these colors now is to print a test print (diagnostic image) that only gives me about 1 sq inch of each color.

When I try to print a light gray from photoshop/illustrator, I seem to never use the light gray ink - uses matte black or regular black. (apparently its trying to outsmart me)

The other purpose, in case you have another suggestion to solve the issue, is that I want to purge the ink and replace it since it might be the ink itself causing the problem. Unless I can print a large area of just those colors Im going to be battling this ink problem a long time!


The printer i am testing this on is an HP Z2100 - though I'm sure the formula is pretty consistent across all printers if its dialed in.

Thanks!
-John