Sorry, I thought you were more well versed in the genetics behind the varieties.
The most important gene towards determining variety is probably the variation (allele in genetics terminology) of the extended black (E) gene. E has a number of variations as compared with blue and cream which each have two variations (blue & not-blue, cream & not-cream).
Light brown (with and without blue and/or cream) is based upon the e+ (wildtype) allele. The only alleles more recessive are e^b (brown) and E^Wh (wheaten) when some combination of melanizers are present.
E is the most dominant of the alleles, but would show up in the parent as a solid (or nearly so) coloured bird. Ditto for E^R (birchen). E^Wh is next in line (usually) and would give a wheaten-based bird. This wouldn't be as obvious on the cock, but female offspring would be wheaten coloured. Next in dominance is the e+ allele which is the base for the variety. e^b comes next.
A bird who is e+/e^b would have the appearance of e+. However, if two birds are e+/e^b, 25% of their offspring would be e^b/e^b. Generally, this would give a bird not too different in appearance to one who is e+/e+, although females would lack the salmon breast. If you add melanizers (which are not well identified/researched), you can create a solid coloured bird. Presumably some could be passed on by each parent, with only a small percentage of birds receiving sufficient to make that solid colouring.
If your pullet is lavender, that still doesn't explain the loss of pattern--it would just further dilute all colouring, but hte pattern would still be there.
