The X-Rite Color Checker Chart is a very common standard used for standardizing different images and imaging systems. (This chart has been known in the past as the Gretag Macbeth ColorChecker Chart,
and the Munsell ColorChecker Chart.) You can take a photo of one chart and a different photo at a different time or on a different system, and then develop a transformation to match the two images based on the colors of the chart's chips.

This script makes (synthesizes) a perfect X-Rite Color Checker Chart from the X-Rite supplied sRGB values. (Note: This script just creates a nice perfect image (which you can save) so it can't be used for standardizing two different images or imaging systems. It's just for looks, for example to put in a publication.) You have options on the size of the image, whether you want informational text (chip name & color) in the overlay, and whether you want to save the image.