Proper mixing of all PCR component is essential for a proper PCR result. In another word some PCR failure may be attributed to improper admixing of PCR mix prior to thermocycling.  Genetek has special Taq, Taq Plus and HS Taq DNA polymerases with special blue, red and orange dyes (named Sky, Rose and Golden respectively) which upon mixing with PCR mix can act as an indicator for proper mixing since the enzyme with the dye will be visible at the bottom of the tube but after proper mixing, one can see if the mixing has been properly done.