Recently, I thought it would be a good idea to create a "test strip" in the margin of one of my photographs.  Here's how to do it:

First, create a white border around your image.  There are several ways to do this, but I use a simple procedure.  Resize the image so as to leave room for the border.  For example, for an 8.5 x 11 print, resize to 7.5 x 10.  Note that you don't want to just crop it to that size.  Use Image > Image Size to actually change the size.  Ensure that your foreground color is black and your background is white.  Then choose Image > Canvas Size and specify the actual paper size (e.g. 8.5 x 11).  Anchor the canvas in the middle, and specify Background for the canvas extension color.  (If the canvas extension color setting is grayed out so that you can't change it, create a new target layer to work on: Control + Shift + Alt + E.)

Next, use the rectangular marquee tool to create a rectangle along the bottom border.  (You can use one of the other borders, with appropriate modifications to the following instructions.)  Now, create a new Gradient adjustment layer.  Make sure the gradient is Foreground to Background, and set the angle to 0 degrees.

Then, create a Posterize adjustment layer, and select between 6 and 10 Levels.  Be sure to select Layer > Create Clipping Mask to limit the posterization to the Gradient Fill layer.  Now select the Gradient Fill layer and double click on it, bringing up the Layer Style menu.  In that menu, select Stroke, and specify a size of about 10 pixels, a fill color of black and a normal blend mode.

With my homemade test strip in the border of my image, I was ready to print.  I have calibrated my monitor.  I am using Epson paper in an Epson printer with the corresponding Epson-supplied profile.  So I was shocked when the test strip on my print was not white, gray and black but variations of a warm brown.  It certainly didn't look brown on my monitor.  In fact, as I moved the cursor from the left of my test strip to the right, the RGB values shown in Photoshop's Info panel when from 0/0/0 to 255/255/255.  Intermediate values were all perfectly balanced grays (e.g. 113/113/113).  I concluded that there must be a problem with the printer or the paper.  Maybe the paper was too old.  I guessed I'd have to buy one of those expensive colorimeters and make my own profiles.  

Meanwhile, I had been ignoring the flashing ink light on my printer.  From long experience, I'd learned that the flashing light meant it was time to by a new cartridge to be prepared when the current one was empty.  I nearly always have new cartridges on hand, so that wasn't a problem.  I knew that when any of the cartridges was actually empty, the ink light would come on solid, and the printer would stop printing.  I've even changed ink cartridges in the middle of a print and couldn't detect the point in the print where it had stopped to wait for me to make the change.  So, I continued to experiment with photo filters, fill layers and other techniques to try to compensate for the brown cast.  The results were mediocre at best.

Then yesterday, the ink light came on solid.  I changed out the cyan cartridge for a new one and proceeded to print a new image, one that I had not added any compensating fill layers or photo filters to, but on which I had created the requisite test strip.  I was expecting to see a brown cast in the test strip and then begin experimenting over again to get rid of it.  To my surprise, the test strip came out black, gray and white without a hint of color cast.  The print looked great!  It then finally dawned on me that the "brown" cast was probably due to a lack of cyan, and that, the result of a nearly empty cartridge, the cyan color had not been applied sufficiently.

The lesson?  No, I'm not going to start changing cartridges as soon as the ink light blinks.  But when the ink light is blinking, I will create test strips to help look for a color cast.  If one shows up, I will change the cartridge before it is completely empty.  What I pay for changing cartridges sooner will be more than compensated for by the time and paper I save.