It may be a monitor problem. Do you calibrate and profile your monitor?
Thanks for the answer ! But no, it's not : even when i print my pdf, the brown color remains.
Finally i think i just managed to find a answer to my probleme : i choose the color profil "Emuler Adobe indesign 2.0"
It fixe my indesign probleme. The greys are back !!
And for the pdf, i choose "no color conversion" when i export my file.
Thx every one !
my whole palette of gray color
What are the gray values? If even RGB (i.e. 128|128|128) or black only CMYK values are previewing as brown then you probably do have a bad monitor profile.