I thought I was beginning to get it . . downloaded ICC's mis-profiled V4 and V2 mountain images to check my apps for V4 and V2 compliance. Extracted their profiles to add to a simple color patch RGBYMC. Sure enough, some apps showed true colors, some did not. Then I noticed something quite odd about Windows Explorer - it showed some thumbnails in true color and some not, even though they had the same embedded profile!
Yep. At right, upper and lower images have Adobe 1998 RGB embedded and show more or less correctly, as one might expect.
At left, the upper and lower images both have ICC's "GBR" profile embedded, which reverses the colors. Yet the upper image shows correctly while the lower is obviously incorrect at BRGMCY.
Thank you Microsoft for making our life so interesting by providing a Windows Explorer which is apparently both color-managed and not color-managed at the same time. Windows XP Pro, SP3. Embedded profiles verified with ExifToolGUI.