UV/Image editor shows wrong colors


When i create image in UV/Image editor (by clicking on “create new image”) and choose some color (for example grey with all color values to 0.5 and alpha 1.0) and then i use eyedropper in material panel (to assign this color to some material or diffuse shader, etc.), i get 0.216 for all colors and not 0.5! I tried to used different color spaces, but result was always same. When i manually write the same values (that i used for new image) for material color, i get very different color.

Please, does anybody know what am i doing wrong?