Excel 2007 : Help with changing font colour if one value is less than 90% of another value

Hello!

I have two columns, one with estimated values (J4:J130), and one with actual values(K4:K130). What I want to do is change the font colour of the actual values if they are less than 90% of the estimated values. Ideally the actual values would become red and remain black if they are 90% or above.

Thanks!