In the generous spirit of this website, let me offer a very inexpensive and simple do-it-yourself color checker.
So earlier today with this idea in mind, I wandered up and down the aisles of Home Depot just looking for the right 'gizmos' to improvise. Suddenly I saw what might work. There is a 4 inch handy hook by Everbilt with a 25 lbs working load limit (that last part not needed
) , This thing seemed ideal since it is already bent into the perfect U shape, has a flat smooth end where you can put your paint sample, is metallic for easy cleaning, and is also a neutral gray tone. The end is curved a bit, not flat, though I doubt that could be an issue for paint matching.
The other end is just a tip of a tube, covered with a rubber cap. Now for a viewer, I went over into plumbing and found a simple black, PVC pipe T connector. About 3 or 4 inches long, it has a nice 'viewing' tube, while the T part at a right angle can be attached to the tube end of the handy hook after I removed the rubber cap. I used some tape to make the actual connection to the tube angle matches the line of sight of the hook end, though I am sure with some refinement, other alternatives to hold it together can be improvised too.
So basically, two parts: the U hook with a flat end, metallic, already gray toned place to put your paint, and a black PVC T connector viewing tube. Total cost, only about $3.