Most of the color papers are coated with various top emulsion cover. For Fuji, it is blue layer.

What does it do? If I understand it correctly, during the pre-wash, this layer is washed away, and the entire emulsion is ready to accept developer chemicals. So it appears this top layer is mainly for protection?

The reason for my asking is that, when I was doing my test printing last time, some of the test strips came out with the un-exposed paper in fainted blue color. That is the same color of the original Fuji color paper. So the top layer was not completely washed away. When I processed the test strips, I pre-wash with warm water for 30 seconds. Then 50 seconds developer and 60 seconds blix. I skipped the final rinse stage and washed the strips in tap water. I normally wash the final prints with rinse chemical for 2 minutes.

I never had the same problem before. So I do not know what had happened. Paper coating change, or chemical change?