Help with RAG status / conditional formatting

Hi
I am a newbie here so please bear with me

I have tried searching the forums for help but do not seem to be able to find a query similar to mine so I really hope I am not duplicating.

I have a list of numbers in column b that are target numbers. Column C will have the actual numbers entered. I would like the cells in column C to turn red green or amber when a number is entered into the cells in column c and based on the following conditions:

If the number entered into column c is is equal to or greater than the value in its adjacent cell in column b = green

If the number entered into column c is 50 to 99% of the value in its adjacent cell in column b = amber

If the number entered into column c is between zero and 50% lower than the value in its adjacent cell in column b = Red

I don't know whether I should be using conditional formatting, IF functions or a mixture of both or whether this is possible without the creation of another column first to work out the percentage calculation between the two values first?

Any help you can offer would be greatly appreciated.