1. They could do, they operated automatically with aerodynamic forces and were not driven in any way. However, it was common practice to push them shut to prevent any foreign matter or debris getting into the mechanism. The Bf 109 sits at a fairly high angle of attack angle on its wheels, very nose high, and because of this they would remain shut, simply due to gravity. If they were not closed then it is entirely possible that one or both might remain deployed.
There is a short and rare segment of colour film of some early Bf 109s which has led some to suggest that the interior colour of the slat itself was the underside colour, in this case RLM 65. I have to say I have looked very closely at that film and I don't find it conclusive. It might not be relevant in 1/72 scale, but in larger scales where it might be visible I tend to do this interior surface in RLM 02 as well.
2. RLM 02 or a continuation of the camouflage colour. I've seen evidence for both, so it would be your choice if you pose the slats (as the devices are properly called in English) deployed.
Cheers
Steve
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