Images as Planes leaving white areas of images looking gray Need some help here, guys.  Pretty new to Blender; I've created a scene (set in a rather gloomy looking tunnel) with warning signs attached to the walls.  The signs were added as images as planes; kept it as simple as possible.  But any part of the images that are supposed to be white look a nasty gray.  Help!

Edit: I've added an image of the light node set-up.  Thanks!

Edit #2: May have inadvertently solved this one myself!  Playing with the ambient occlusion settings is allowing me to bring out the white of the images!  Now to just get the settings right so my tunnel scene doesn't look too bright!

[![Material nodes][1]][1]
Colors are directly relative to light, your "white" value is determined by the color of the texture but by the light too (colors are just parts of light spectrum not absorbed).
For the diffuse part, RGB of 0.8 means that the surface diffuse 80% of the light it recieved.
For exemple pure red means (in RGB values) that green and blue are absorbed R=1 G=0 B=0.
Just to let you know there isn't any materials that returns 100% of the light it recieved.

3D rendering needs knowledge about light and photographie, I recommande you to read about this two topics.
There is a good doc about physically based rendering by Allegorithmic that you can read too.  

Edit your question to add pictures if you can, I don't remember if you have the right when you start here.