Assuming that they are apparently healthy and have no obvious flaws, a generation or two won''t hurt. Alternatively, you could get unrelated birds to have multiple initial breeding pairs, resulting in sets of F1s that are unrelated, then breed birds from one set with birds from another.
Are you sure that isn't cochilks?
Anyways, there is no predicting the colour other than there are unlikely to be either white or lavender offspring. Lavenders must inherit the lav gene from each parent to be lavender, and unless the white has lavender in its background, the presence of the...