I have a question , what color should i get from my exchequer leghorn rooster and my milli fleur leghorn hens,
I am not a genetics expert... This is what I know...
Since the American Poultry Association does not recognize either color variation of Leghorn, unless you got both from a very reputable breeder, there is no solid guarantee that your mille fleur or exchequer will breed true.
Now, exchequer Leghorns likely have the mottling gene (which mille fleurs also have). Given that, the offspring are likely to be mottled. Additionally, Exchequer leghorns have the 'silver' gene and the 'extended black' gene (from what I have researched). The silver gene is a dominate white gene (making at least some white show up in the offspring) and the extended black results in black based offspring (this gives the black background color with the white showing through).
Given that, the most I can do is guess that the result will be mottled (possibly mille fleur) with a dark base color (possibly depending on what kind of mille fleur you have: mahogany, buff or red based). Since 'Exchequers' are typically not mottled as symmetrically as the 'mottled' color or mille fleur (a type of mottling), you might end up with a mille fleur pattern that is less even.
However, as I said, that is largely just a guess from what I have read about both color variations.
