Actively looking for rainbows in this way will almost guarantee that anyone will see them. As you say you don't see them when watching films which is what is important. I would recommend just watching some material that you are familiar with and don't try to force youself to see rainbows.
If DLP doesn't agree with you then I would think it would be obvious without having to make yourself have problems with it. Personally I occassionally catch a glimpse of a rainbow during a dark scence but other than that I never have a problem.