The answer to your question would be that the past perfect progressive form of suggest to complete the sentence above is the following one: Had been suggesting. That is, the correct option would be A.
The past perfect progressive, also called past perfect continous, is a verb tense which is used to show that an action started in the past and continued up to another point in the past. In this case, the action (suggesting changes) continued up until the lunchroom was finally repainted.