Let’s say you want some guidelines on your paper when drawing or writing. Gridlines to make sure everything is lined up. You could use one base color for the gridlines, and then remove that one color in Photoshop. It’s a trick that comic strip artists use. They first draw with a cyan pencil, and then ink the drawing in with black ink. When the comic is scanned in, they can easily remove the cyan color in Photoshop.
When I print a 50% cyan line on my printer, it actually prints out some magenta and yellow dots.

See those little magenta and yellow dots. What are they doing there?
This is a little odd, because cyan is simply cyan. Printers use four colors when printing: cyan, magenta, yellow, and black. When you want cyan, the printer should use only cyan ink. There is no magenta or yellow ink to create the cyan color.
It’s a little disappointing, because I want to use my custom graph paper as guidelines when handwriting Bible verses.

In theory, in Photoshop I should be able to easily remove the cyan by simply removing the cyan channel. The cyan magically disappears, leaving my pencil lines untouched.
But now there are these pesky cyan and yellow dots leaving marks behind.
I’m going to see if there are settings on my printer that allow me to print using ONLY cyan ink.
My twin brother, unlikelymoose, had some suggestions for me via text:
It’s probably a safe bet that it’s just the printer doing its own interpretation of how “50% cyan” should be printed. But it might be worth a try to print from different programs.
One idea is you could try a more teal color. Maybe that will remove the magenta. It’s better to be dealing with an excess of yellow dots than magenta dots.
I’ll give those tips a shot too.
If you’d like to give it a try, here is my 8.5×11 gridlines file in PDF format.
What you’re running into might be the anti-counterfeiting “feature” included in many printers today. Small yellow dots are used to encode the printer’s serial number and a time/date stamp. If you try to print fake money, the Feds will use the encoded yellow dots to track you down.