Hi, I noticed this, but not sure why.
Adding a decal changes the colour of the surface in Raytraced view. As seen in Fig1, the surface with decal is turns darker than the usual (the small rectangle, split from the surface is the original). This could be replicated with an empty .png file.
Fig2 shows the effect when decal is removed. Fig3 is just for information.
Material has not been changed throughout (plastic in this case). Using SR14.