As I have well explained in a previous post ( Gels, Filters and Good Color and in more detail in Beauty Shots? Glamour? Style? ) there is a difference between good color and accurate color. That said getting accurate color to start or at least be able to set accurate color in camera and then alter with gels/filters on the lights or camera is an important aspect of being in total control of your image making process. Here I will detail some of the steps I take to be in full control from capture to print.
To start I use several devices, the WhiBal had always been my WB reference of choice and I still use it today along with other new devices. To see why the whibal is more accurate than a standard gray card or white paper refer to Michael Tapes video here WhiBal Now why use anything more? Well that only helps to set an accurate white balance, it does not help with color reproduction and saturation, so what I use today which does help to create an accurate base and camera profile which can then be matched across cameras for WB, color tone and saturation is the X-Rite Color Checker Passport and profile software. To see what that can do for you check out this video by Seth Resnick, also a Canon Explorer of Light with great color work, Color Checker Passport Video
Once you have good color in capture and make a custom profile for the raw conversion make sure you have a calibrated monitor and printer. A good starting point on that whole system is this video (its long, but well worth the time to watch) Webinar: Color Workflow for the Photographer It is from one company, and I do recommend their products, but the information can and does apply to any brand of calibration hardware you use.
A standard color checker is also built into the X-Rite Color Check Passport as well as neutral gray patches and warm and cool tone offsets. On the color checker chart its been claimed that the second lightest gray patch is the ideal for white balance on a color chart. In an ideal world, any gray patch should work just as well. For more on good vs. accurate color and altering color in camera I do suggest you read the following two posts: Gels, Filters and Good Color and in more detail in Beauty Shots? Glamour? Style?
So when the color checker passport does so much, why still use something like a whibal? Size, its easy to fill the frame with the whibal and shoot a in camera Custom WB (not needed for raw, but its nice to have all the previews looking the way you sort of want them too) For this its just more practical to set a custom white balance in camera by easily filling the frame with the card and setting it in camera, (good for jpg shooters and also saves the hassle of having to click balance later in raw)
I use a dedicated card to set WB in camera and I use it often to offset white balance through the use of a wratten filter over the lens to register a cooler tone in camera then what will be present once the wratten is removed. This whole procedure is described in detail in the above posts on color.