The geography in Northern Europe had much to do with the color and medium that Renaissance artists used. Oil paint was used as early as the twelfth century in Northern Europe but flourished after famous artists perfected the technique. 
Using oil paint offered artists much flexibility in their color and composition. It was slow drying and easy to layer, which allowed artists to paint longer strokes and blend colors together. 
Jewels and metals, such as lapis lazuli and gold, were used to mix with the oil and apply to the painting, giving them metallic and vibrant colors. 
These colors were very expensive; only wealthy patrons could afford to buy them for their artist to use, but they gave the paintings an extra sense of depth and opulence. The oil paint was much more realistic than the tempera used in Italy. Artists in Northern Europe could create highly realistic shadows and physical proportions with the strategic use of oil paint. 
For example, an artist in Northern Italy could easily replicate the shadows required to show muscle tone in a figure's stomach or arms using shading with oil paint.
The detail that oil paint allowed made portraiture very popular during the art renaissance. Artists could accurately capture a patron's figure and face using oil paint. 
Famous artists, such as Jan Van Eyck, were commissioned by royal courts across Northern Europe to provide portraits of the nobility.