If you want to evaluate color reproduction and accuracy, you need to use a color checker card. X-Rite is pretty much the source for such devices today, as they purchased Gretag Macbeth some time ago. I personally use the X-Rite ColorChecker Passport, which is a handy pocket-sized clamshell device with the standard colorchecker pattern, an enhanced color calibration chart, and an 18% gray card inside. You can also get a larger "standardized" colorchecker pattern chart with the standard pattern, a large extended pattern chart (with LOTS more color swatches), and a few other options. I would say the standard pattern is plenty.

You just set the color checker card up in a known lighting type, say sunlight, set the camera's WB setting to match, and take shots under each picture style. You can then compare the results of these on your computer screen to the actual card (just hold it up to next to the replications on-sceen.) I believe these days there are also digital versions of the color checker card that can be used for comparison purposes as well, although you need to make sure you calibrate your screen appropriately so as not to skew the digital version. (Really, you should probably calibrate your screen to a normalized medium anyway...I would check X-Rite's site for proper use of their color checker card, as it has been quite some time since I did all this calibration myself.)

You should be able to readily perceive differences in color reproduction and saturation for each camera setting. Its also important to keep in mind, the tool you use for RAW processing, if you wish to check RAW, will affect color reproduction as well. Most, such as LR/ACR, Aperture, etc. have their own approximations of in-camera picture styles, but they are rarely exact. You will need to use manufacturer-provided tools for the closest RAW replication of in-camera JPEG picture styles. You should be able to compare similar settings for your Pentax as well, and see how both cameras fare relative to the standardized swatches themselves, as well as to each other.