Currently I have a gray car and you can't see the dirt unless you are right up on it, however I wash my car at least every other week.
With that said I would not go with black since it is the worst with showing dirt. The sterling gray would be an excellent choice. Ingot silver and maybe the red candy would be a good choice.
Personally, I would just wash the car more and get the color you really want or take it to a car wash to keep it relatively clean.
'66 Coupe 200 cu in | Candy Apple Red | Black Interior | Rally lights | A/C
'12 VW GTI 4 dr | DSG | Neuspeed P-flo intake | pushing 225 whp
SOLD '11 GT Prem Kona Blue | Saddle | Sec Pkg | Brembos | had many mods