Abstract: The invention relates to the use of sterically hindered piperidine derivatives (HA(L)S) in pigmented polyolefin polymers for the reduction of warpage effects which are induced by light. Preferably, such sterically hindered piperidine derivatives/amines (HA(L)S) are used in various combinations with UV absorbers, processing stabilisers, phenol-type antioxidants and acid scavengers normally used for the purpose of improved lightfastness and improved mechanical properties. In particular the invention relates to a method to reduce the warpage effect which is induced by light in polyolefin polymers, comprising the steps of combining in the polyolefin polymer at least one organic pigment and at least one sterically hindered piperidine derivative (HA(L)S).