In the burning of Pb(NO₃)², what will be the change in colour of lead oxide?

Lead Nitrate decomposes on heating as follows.

2 Pb(NO3)2??Heat???2PbO + 4NO2+ O2

Here the?PbO formed will be, Yellow in the hot condition and white when cold.

The reaction should be carried out on a dry condition,if not the Nitrogen dioxide or Nitrogen Peroxide formed will dissolve in the water or moisture present in the test tube, to form nitric and nitrous acid.

2NO2 + H2O ????-> HNO3 + HNO2

Lead nitrate on heating decomposes to lead monoxide, nitrogen dioxide and oxygen. NO₂ is liberated, along with oxygen, as a reddish-brown gas. The residue left is lead monoxide(PbO). It's yellow when hot and white when cold.
2Pb(NO₃)₂ (s) → 2PbO (s) + 4NO₂ (g) + O₂ (g)

Hope this  helps :)