How do I colour fill cells in Column A based on values in Column B

I assume that you are familiar with conditional formatting.
Select Column A and create three Conditional formats.

1: Formulas as specified. However 30 and 70 remain uncoloured.
Conditional format formula for Green =$B1>70

Conditional format formula for Yellow =AND($B1>=31,$B1<=69)

Conditional format formula for Red =$B1<30


2. Better Formula.
Conditional format formula for Green =$B1>70

Conditional format formula for Yellow =AND($B1>=30,$B1<=70)

Conditional format formula for Red =$B1<30


3: Conditional Formatting

click on the A at the top of excel to select all cells in Column A

Select the home tab and then conditional formats

Select New Rule

Select Use Formula to determine formatting

Enter the formulas into the formula box


Select format

Select Fill

Select the colour you want.

Press Ok until you get out of conditional formatting.