The colour of a diamond is one of the most important factors that affects the value of the stone. Diamond colour is graded according to the GIA (Gemoligical institute of America) colour scale which runs alphabetically starting from D to Z±, with D being the highest and most desirable. As the scale goes on, the colours become more yellow which decreases the value of the stone.
Diamonds that are said to contain flurescense contain particles that give a blueish glow to the stone when exposed to UV lighting. However, fluorescence is not a factor when assesing the colour or clarity of a diamond, but it does decrease the value of the stone.