A word of warning though. Every printer is different. Make sure you use photo paper and high quality printing mode on your printer. Even then, the cards might not come out right. You have very little to lose though. If the cards don't print well, you can still opt to buy the wooden cards from Montessori shops.
Download and print these three PDF files:
You can also download the SVG files I have created using Inkscape and subsequently exported into the above PDF files. SVG files might be useful if you want to edit the colors a bit.
I've gone overboard and printed the cards twice, then laminated them together to get nice two-sided cards. I can confirm this is unnecessary and sometimes counterproductive as the laminated cards reflect light under certain angles. You will be better off just printing them one-sided on quality paper, then cutting them. If some of them get damaged, you can easily print new ones.
While playing with this project, I noticed how hard it is these days to get quality color output on cheap home printers. What I see on the screen is not what I see on paper. Color spaces are standardized, but manufacturers of monitors and printers nevertheless prefer to use their own oversaturated uncalibrated colors.
That's why the shade ranges in my cards are sometimes so narrow. Ink printers usually cannot print pale green and similar colors that mix basic CMYK colors in very small amounts. Interestingly, the commercially available color cards on wooden blocks have similarly limited ranges of tints and shades. I guess LCD screens might be better for showing kids color spaces as they have much wider range than printers. Some Monte teachers might wish to reevaluate their negative stance towards computers.