Solid black shows scratches very badly and I suspect could be the worst possible colour for resale. Solid red has a tendence to fade and will certainly make resale difficult as the car gets older (5yrs+). It requires a lot of waxing to avoid this. I'm a little biased but I think Candy White is the only solid colour to seriously consider and it simply looks amazing (in 5dr as well as 3dr). There are very few cars white works on but the Golf GTI is close to top of the list (alongside a very select group including the 911 GT3). Many journos have pointed this out and on the right cars its the colour of the moment. In my case, the very attractive spec and price made me brave I'll admit.
If you must go for black then I think it has to be pearl. Otherwise that mid blue metallic looks very good IMHO and is also rare. I have a suspicion it could be the Oak Green (an iconic mk2 colour) of the future.
Jon