As riggers, we have to inspect bartacks and other stitching, regardless of color. Grey thread on white shows up plenty well enough to inspect. If it is too hard for a rigger to inspect grey thread on white spectra, or for that matter white thread on white F-111, then you shouldn't be a rigger.
I know most thorough riggers have some sort of checklist like this. At Chuting Star Rigging Loft, we have a 1/2 page checklist that covers all components of the harness, container, reserve and AAD. All components are checked at assembly AND repack. This missing bartack should have been caught...no exscuse if the last rigger assembled it or repacked it. ChutingStar.com