about diamonds weight and clarity?

i want to know in diamonds which colour is considered colouerless i know d and e and f but for astrological purpose which colour to go for ninety nine percent people cant buy d and e and f and what clarity scale in which there will be no red or black spots and is cut important please advice and above all can two diamonds to wear instead of one because more the weight more costly example if i need to wear 1 carat can i wear two peices of .50 cent each because it will cost me far less then peice of 1 carat pls answer then only i will go for my diamond after getting my answer on yahoo answers

white diamonds

Diamond Color Scale