pressure washed house and darker areas appeared.. why?

Recently had my house pressure washed. I had noticed some darker shading appearing where the roof condensation was the last to evaporate in the mornings, however after the house was washed those areas seemed even darker than before. Our homes exterior is a combination of cedar trim, hardi plank and brick. I know that bleach was not used and I am not sure if it was a chemical reaction to whatever detergent was used or what? Not every where that the house was washed has darkened only certain areas that do not get as much sun. I have tried to contact my roofing contractor but he has gone out of business. My contract says galvalume steel roof, but does not specify the manufacturer for me to call and ask questions. Is this shading normal or how do you get this off of the roof? To the touch it does not feel like dirt, very smooth. If you spray with a harder pressure washer attachment the color lightens? Why?

Feel free to email me picture sif you wish but this probably is normal for the roofing you have. tmiller@classicroof.com