Power washing is a wonderful tool, IF used properly and for the right job.
I am speculating, but I have seen this too many times. The PSI was too high on the washer or the operator was too close with the high pressure water.
I imagine that the streaks you are seeing is the primer or some under coating from the factory bleeding through.
Did you contract the home to only be washed or washed and then painted? If only to be washed, you might have some legal remedy from the washing operator. Take pictures and document the situation. It could just also be an accident.
Anyway, you now need a paint job. Research the best paint for your situation. Shop paint dealers not, not home centers or hardware stores.
Apply a good primer and you are ready to paint. Make sure the surface is not chalky. If so, add an additive to the paint for this problem.
I do not want to lay any blame anywhere, the Power Washing could have just been the catalist that brought down the finish coat before mother nature did the same thing. If your siding is old, then this could have been just the time. Newer siding has a baked on finish like your car's finish and will tend not to do this with time.