The more colorless a diamond the greater its rarity and value.

The diamond color scale begins with D [whitest] and descends to Z [considerable yellow].

The GIA describes color as follows:

We recommend colors in the "D to J" range because these colors are more beautiful and historically have increased in value more rapidly.

Two diamonds with the same GIA color grades will not necessarily face up exactly the same. Every diamond will reflect color and brilliance in its own unique way. 

Interestingly, the same diamond submitted to the GIA for color grading more than once will not necessarily receive the same grade each time. Why? 

Color is graded on a spectrum and is ultimately a human and subjective call. Within reason [one color] it is understandable for a color grade to be seen slightly differently by different graders at different times.  

A diamond selected in the D to H color range will not show any yellow tint while colors I and J might have just a hint.