Right so your talking about the drying van vent on the front of the control panel, apologies I thought you were referring to the inner-side of the door.
It sounds like the waste pump hasnt removed all the residual water, before the drying fan has started, have you cleaned the sump filter and removed the plate and given them a good clean as per the page 34 of the manual here?
The residual water is then being blown into the air duct, which is then making it into the door vent, the colour could be partly because the vent has dust and dirt which tainted the water or just because the waste water hasnt been fully pumped out and being dirty to start with.
If after the filter and sump plate have been cleaned the fault is still present, the next stage is to check the waste pipe at the rear isnt kinked, and the drain has good flow, after which its a case of getting someone in to test the pump, and flow regulator which tells the pump when to stop.
With regard to the rust, I would give this a good clean off with vinegar, and most like caused due to the amount of water left in the machine when not in use.
Should you like me to recommend someone to come to site to look at the pump please provide your postcode.