I buy aluminium sheet already anodised as this is a tricky process involving acids and electric currents. The next stage is the dyeing which is where the creativity comes in. Special dyes and inks are used to create patterns or plain areas of colour. All sorts of interesting techniques can be used including printing, painting or drawing on the surface. When the design is finished it is sealed by boiling the metal which fixes the colour making it permanent.
The nice thing about Aluminium is that it doesn't tarnish, so if it ever needs cleaning just use a soft cloth and some soapy water. If the piece is Aluminium and Silver just use a silver cloth. Please note immersion in silver cleaning liquids may remove colour from the aluminium.