I believe the color of the infringing meters was deliberately chosen, although Sparkfun was probably not aware of the trademark. I use Flukes and didn't know the coloring was protected.
However, how wide is the range of yellow that is considered to infringe on Fluke's special yellow? How many such ranges can be trademarked before no one can manufacture a solid colored meter boot without infringing on some trademark color.
I suppose at that point we move to stripes, ginghams and paisleys.