Try this:
Select all the date cells, not just a single column, then enter the following 3 formulas for the conditional format:
=OR(WEEKDAY(B2)=1,WEEKDAY(B2)=7) Format as Dark Grey
=AND(B2<TODAY(),WEEKDAY(B2)<>1,WEEKDAY(B2)<>7) Format as Light Grey
=AND(B2=TODAY(),WEEKDAY(B2)<>1,WEEKDAY(B2)<>7) Format as Yellow