Question

when we add potassium permanent to pine oil colour change that we observed in solution

Answer 1

KMnO4 is pink in a solution without oxidizing reagents. Adding ethanol should change it to a brown solution. If adding ethanol can not change the solution to brown, then its environment is already acidic and will not reduce.

When potassium permanganate reacts with ethanol, it releases nascent oxygen. ie, an atom of oxygen thus converting the ethanol to acetic acid. Initially colour disappears because coloured permanganate ions of potassium permanganate are consumed to oxidise ethanol.

C2H5OH  (WITH ALKALINE KMnO4)    CH3COOH+H2O  

When excess is added colour does not change because there is no more alcohol left and hence there is no reaction.