the invention relates to a method of preparing a reaction mixture for polymerase chain reaction assay and a solution set for pcr . the method comprises providing a sample solution comprising a biological sample to be amplified in said pcr assay and first colorant providing the solution a first color , providing a reagent solution comprising at least one other substance required for performing said assay and second colorant providing the solution a second color different from the first color , and mixing the sample solution and the first reagent solution for providing a mixed solution to be subjected to the pcr process , the mixed solution having , due to said first and second colorants , a third color different from the first and second colors . the invention significantly aids in pipetting pcr assays .