Colour blocking is a fashion trend that comes and goes. It was made famous in the 1964 jersey day dress by designer Yves St. Laurent.
Colour blocking recently reappeared on the runways in 2011 and is becoming more and more mainstream. Colour blocking in fashion is defined as using bold adjacent or complementary colours in a single look. It can achieved by combining separates and accessories or stitching together various colours into one garment.
Variations on colour blocking involve using tints or shades of the same colour, pastels, black, white and greys or even prints.
Colour blocking is risky because it is attention-getting and can easily be done wrong. Even the experts are struggling to pull off this look. Unless you have a really good eye for combining colours, a refresher on colour theory is probably warranted.
Tiger Colour has an excellent basic introduction to colour theory. Visit this website to read up on it.