This is a little off topic for this board, but…
I am trying to set up jpeg files in Photoshop with 6 rectangular blocks: the RGB primaries, white, mid gray, and black. I save these files at the lowest compression. The file type is limited because I need to use these in web pages.
When I reopen the files, the primaries are off. I get values like (RGB(254,0,0) and RGB(0,255,1). It happens in sRGB, AdobeRGB, and ProPhotoRGB.
Is there any way I can avoid this? Would GIF work instead of jpeg?