Cannot set color to pure white.

Cannot set foreground color or background color to pure white (255,255,255; #FFFFFF). No matter if I select from a palette, pick color from the screen, or type in the RGB or HTML values, HyperSnap (v8.16.16) reverts to some off-white color (252,254,252; #FCFEFC). The color is close to white, but when added to a document with pure-white background color, the off-white color is obvious.
 
This happens for both GIF and PNG formats that I've tried. Oddly, does not happen for all files (some 'allow' pure white). I tried saving the affected files with a different filename, changing from GIF to PNG, for example, but problem remains. I also tried filling an area with a totally different color (bright green) and then re-fill with pure-white ... but HyperSnap reverts to the same off-white (252,254,252) color.

Works if I increase the color resolution to 32 bits, for example. But begs the question why can't I use 8 bit color resolution if I'm only using very-basic colors? I tried creating a new image. If I set 8 bit color, I can't achieve Windows-basic 'white' even for a white square with just that one color. HyperSnap seems to force "Optimized" color palette and won't keep "Std. Windows" palette selection.
 
For my real image / example, I took an older, very simple image with 8-bit color resolution that looked fine, originally, with pure-white background. But once I edited it with HyperSnap, it seems an 'optimized' color palette was applied and substituted some off-white for my original white.
 
 - Why can't I apply 'Std.Windows' color palette?
 - Can I see (and edit) this 'optimized' palette to possibly substitute colors (off-white for white, example)?