Your question can be divided into two.
- Maybe you are not satisfied with the appearance color of the food safety detectors. Just talk to your supplier and tell them how bright you want. For example, you can use a PANTONE number to specify the color type. There is no extra mould cost since you just change the color.
- Darker color is not the implication of bad quality of PCB. Test report of the product and quality management is very important. Ask your supplier for final product test report. Or, you can send it to the professional testing lab, but it means additional cost.
- Visit that suppliers in site. A good factory should have automatic product lines, an R&D team, a QA team and a series of certifications. These are also the factors that contributes to stable quality of batch production.