The 127 127 127 is the middle color of the grey  scale of red, this is  in the middle between the white and black color , that set up the model surface this way that the HDR Light probe you use to light up the scene will not expose the textures you rendering on your model, this way you can change the intensity of the HDR IBL light up and down and have always a nice effect in your renders as I do always in mine.. the green for example would be a green and not turn into yellow or fade out in bad way.. you can compare the bad effect to exposed to much to light pictures.. for example if you make a real picture sometimes the sky is so bright almost white but only on your picture b/c as you remember the sky was blue for real.. thanks to HDR you can balance the image and show it as it was for real... a true high dynamic hdr images are composed from minimal 26 images that are made with different F-stop to get the 99% effect as we see with our eyes in real world, this capture the true light and shadows into one image..and after that we can use it to light the scenes to get more realistic renders.. if you wanna make a own hdr for light probe to use in poser7, you should use minimal 3 photos of your mirror ball wih different exposure, most of the cameras today have this setting automatic, so one click and you are done.. after that you can work in photoshop CS3 and merge them together crop out the ball from the final hdr image and ready to use in poser.. this way your background photo you load into poser scene will match the light in your scene and blend the models into the 2d world.. this is the simple way if you work with photos to capture the light... if you have not true mirror ball use just a silver christmas ball ... look at the pic above,  that was made the way I say..

_________________________________________________________

"Surrender to what it is - Let go of what was - Have faith in what will be "