diff --git a/apps/tutorials/pe/02_ConfinedGasExtended.cfg b/apps/tutorials/pe/02_ConfinedGasExtended.cfg
index 1e1b9eb004a06fb94697ee26020344eeed99cf0a..f06e81138cd2e4f879e6d1f04d6267e279ea4598 100644
--- a/apps/tutorials/pe/02_ConfinedGasExtended.cfg
+++ b/apps/tutorials/pe/02_ConfinedGasExtended.cfg
@@ -21,6 +21,7 @@ Raytracing
    upVector < 0, 0, 1 >;
    antiAliasFactor 2;
    reductionMethod MPI_REDUCE;
+   backgroundColor < 0.18, 0.18, 0.18 >;
    Lighting {
       pointLightOrigin < -10, 10, 15 >;
       ambientColor < 0.3, 0.3, 0.3 >;