Without a direct comparison with stones of the color grade D-E (River) and F-G (Top Wesselton) one sees no difference. Wesselton diamonds are less expensive than higher color grades, but just as well cut and sparkling as these. 
 
Wesselton (new designation: H) is the diamond color for 'white'.
 
What do the clarities mean?
The basis is the view through the 10x magnifying glass:
 
No inclusions are visible at 10x magnification, the stone is flawless (LC) or IF (internally flawless)
 
If inclusions are (very) difficult to detect, the purity is referred to as VVS = very very small inclusions or VS = very small inclusions
 
If inclusions are visible at 10x magnification, this is referred to as SI = small inclusions
 
Noticeable inclusions begin with the designation P1 and end at P3.