You can hit the right colour just using a small amount of black malt but it won't taste the same as a brew which gets the colour from crystal or toasted malts. The different shades of crystal have their own flavours ranging from light caramel and nuts through to dark toffee, raisin and other dark fruit flavours.
I brewed a bock last night which is a strong (fairly dark) amber lager, 3kg each of golden promise (5 ebc) and Munich II (22 ebc), 250g each of melanoidin (60 ebc), CaraMunich II (120 ebc) and CaraAroma (400 ebc). So that gives me a lot of bready flavour from the 2 base malts then a mix of honey, toast, toffee and dried fruit from the blend of speciality malts, CaraAroma might even give a hint of roast since it's so dark.
I also get colour (and extra flavours) from boiling down 3L of the first runnings to a thick syrup, around 500ml, this concentrated boil makes the syrup very dark so it's like adding dark candi syrup to a belgian beer.
Good luck.