Simply put, there are two common ways of expressing color in computers:
linear, where the number in the file is directly proportional to the brightness
nonlinear aka gamma corrected where numbers are optimized for display purposes on monitors

The dilemma is that all math in render engines implies linear data, where most common file formats are non-linear. So Poser does it in several steps:

1. It has a first step where it converts non-linear textures to linear data.
2. Then it renders in an all linear color space.
3. Then it applies gamma correction as necessary to the linear data it gets from rendering to save it to image files and to show it in the output window.