The validation stage in the projects I work on is an important stage. In this case (which is anonymized due to NDA issues), we had a short deadline for delivering an MVP and a design testing stage had been disregarded by the sponsor. Even so, we had great results when including the end users before delivering the project of a mobile solution to evaluate the attendance of a technical service.
We had planned a five-level satisfaction scale based on Likert, where the closer to 5 the more satisfied the end customer would be with the service.
We were not sure whether using a color scale would help or not in making the user’s decision about which option he would choose, so we recruited some people who were within the solution’s user profile and, in pairs, we asked them to perform a task.
We found that, not only did colors not help in decision making, but they hinder users. We also found that they felt more comfortable using letters (they felt it was more neutral and less influenced) than using the numbers from 1 to 5. So, we changed the interface and the end result has been well accepted.
We did the test with approximated ten users and we make sure that we had at least one color blind person in the group, after all, the test included color issues.
I wrote and publish about this process in the portuguese page of uxdesign.cc too.