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The red is from water and soap getting under the siding and reacting to the ink on the weather wrap or something else under the siding.
In our experence the fading is from to much bleach on the paint. Next time tune it down a bit.
Have you tried rinsing it really, really well. When its wet can you brush off the marks. Try brushing it if you can, I know its a pain in the arse but better than a repaint unless you want insurance to take care it.
What did the H/O say about just curious.