How to blend colors?

If you need to keep each layer as pure C M Y or K, and this may even easier, is to just make 4 copies of your CMYK image, then open each and FILL each of the other channels with White. like so;

Not sure what exactly you want to do, but I am going to assume what you're looking for is a way to create the 4 (not 3) acetates like they have done for the image on this page for your own image so you can print out similar transparencies.

There are few ways to accomplish what you want. this is just one way (I'm sure other will jump in with other ways). First, you need to convert your image to CMYK mode if it isn't already. Also, in your Photoshop > Interface Preferences, check the button near the botton to Show Channels in Color.

Make 3 extra copies of the file. In the first copy (to make the Cyan copy), open your Channels panel, then select and delete the M, Y and K channels. This just leaves the Cyan channel. Export this as a JPG. It will be in RGB, but chances are you are printing to an RGB-based printer so it doesn't matter too much. Do the same for the other 3 colors, deleteing the 3 channels you don't need in each.