Trademarking a color is pretty relavant and quite reasonable from Park's perspective. Anyone who is familiar with bicycle tools would recognize that color as Park's, and the site of blue tools on someone's bench or toolbox gives you the signal that they are using quality tools. ON the other hand, if every knock off company began making tools in the same color, or with similar markings, you couldn't rely on the site of blue tools to be that of a quality tool, thus the park tool becomes either less recognizable, or they simply lose their association with quality products simply by color alone.
Companies have been trademarking colors for a very long time because very often there is alot of good will associated with a certain color or color combination. Fast food restaurants have litigated over seemingly innocuous things like color combinations of benches and tables because they feel there is that much brand association wrapped up in such things.
In the case here, it's pretty obvious. I suspect that many of us clicked the link and either thought, wow, park tools for 35 bucks! or wow, those tools really look like park tools. Either way, most of us, weather we admit it or not, quickly associated those tools in the link to Park tools.
Whatever.