Question

aag pila colour me hi kyo jalta hai

Answer 1

This is due to incandescence of very fine soot particles that are produced in the flame. With increasing oxygen supply, less black body-radiating soot is produced due to a more complete combustion and the reaction creates enough energy to excite and ionize gas molecules in the flame, leading to a blue appearance.

Answer 2

because it is it's nature feature.
May be this answer will help ypu