Decals are darker than they should be.

I’m having an issue with decals applied to a static mesh. The decals look fine on the sunny side of the mesh, but get dark on the unlit side. Here’s a sample screenshot:


The thing is the decal in the picture is actually bright white, yet it appears much darker than the material it’s applied to which is a medium grey. It seems the decal is ignoring indirect lighting. Is there a setting which can fix this?