Looks a tad dark, but if you tried to go lighter, it could look too light...if you know what I mean!?! Allowing for the angle it'll be seen at behind the windscreen, I reckon it'll be OK. if you decide to go lighter (probably have to make a new screen), I've found that adding a touch of gloss clear to the 'paint' works quite well, and is more controllable than trying to thin the transparent paint.
Yep, the skid, or slip marks were to indicate if there had been any major movement of the tyre on the wheel rim, probably caused by heavy landings or agressive braking, which could cause the tyre carcass to move, but leave the tyre bead itself more or less in the same setting, or even just break the bead seal, causing deflation. The former would lead to stretching and stress of the tire wall and bead, which in turn could cause failure of the tyre, leading to possible major or total damage to the aircraft. These markings are still used today, normally in yellow, and often at more than one point on each wheel/tyre.