

Perhaps its the chosen colors bud. Maybe if you used a difference thats more extreme. I mean, If the engine must see textures differently because of the lack of light, maybe its the components "OF" the light that are the issue.
Light is composed of colors, if your light, or lack of light has colors that clash with your chosen ones then they will, or may cancel each other out.
Its just a theory, but try altering the light spectrum, or the colors on the wall.
*shrugs*
good luck.. sorry I am just an idiot. :/

looks fine to me...
but if you want, just use the curve tool in photoshop (I assume you use it) and drag the line so it makes an S type shape. This will bump up the contrast and give you more defined colors.
