Partridge boys are the easiest to sex early because of their dark, deep, and varied shades of color. I think they will start to grow some black tail streamers which the girls don't get very dark if at all. As for the other colors, wait until they crow or lay an egg LOL.
6-mo female Partridge -- not a lot of shiny or dark colors
6-mo Partridge male with varied and deep shiny colorful shades
Plain softly colored pullet with multi-colored cockerel
Colorful partridge cockerel, dull Partridge pullet (White Leghorn pullet)