Calculation and Colour Logic.

Hi , I am stuck with some logic here in color code, I need to represent variance column in amber colour ,if the varience is dropped to 50%. than actual value, Now this variance column is calculated with formula (actual-cov.threshold)/actual*100 so getting value is.How would I calculate that?I have used richtextDisplayfield

 a!richTextDisplayField(
              value: a!richTextItem(
                text: fv!item.varience_txt,
                color: if(
                  fv!item.varience_txt < 0,
                  "NEGATIVE",
                  if(
                    fv!item.varience_txt > 0,
                    "POSITIVE",
                    if(
                      (fv!item.varience_txt) < (fv!item.actualThreshold_txt * 0.5),
                      "#FFBF00",
                      ""
                    )
                  )
                )
              )
            )