Rach 123, Sorry, I answered your questions, but it posted twice, and when I tried to delete one, apparently it wiped out both!
Your very pretty Dutch is not a variety at all, but a mix of varieties that are not compatible. Buff/Speckled? Is that a Lemon Mille Fleur? If so, to breed DUTCH, she would have to be mated with a Lemon Mille Fleur or a Mille Fleur--no other cross will produce an accepted DUTCH. And like Vegetable soup, with many colors of veggies, you cannot return a soup to its basic broth, by removing a carrot or a tomato--once the veggie is put in, it always leaves its residue color. (paraphrase from Sigi van Dort's book (GENETICS of CHICKEN COLOURS) That is the best explanation of why you cannot cross varieties (colours) that are not compatible. So your lovely colored cockerel cannot lose his "additional genes for color" by any cross you choose--only will add more veggies to any offspring, that will be useless to produce any variety--only attractive "pet backyard banties" and not Dutch.
Your Lavender male should be crossed only with Lavender or Black Dutch--although by many generations of work, with most offspring having to be discarded, there are now, Lavender Cuckoo and several other" Lavender" varieties that are approved in Holland, and can be shown in Holland--and perhaps in UK?. Takes generations and years of work to make a new variety in any breed of Bantam.. Few of us have the space nor can afford the expense of feeding to mature color, the numbers of birds to attain a "pure" new variety."(and know its genetic code).
So your lovely cockerel, would not have a class to enter at a Show. In the UK, To be a Blue Partridge, he would have no red except his back (and red orange) and wing bar, and yes, he would have a blue breast AOC accepts those named varieties that that are approved by the UK Poultry Association. In the US, we have no class as AOC, so without a known variety name, a bird (even a Dutch cross) will not be judged at all. Difficult to get a new variety approved. (Recent Scottish National Show had a great entry and would be a good Show to attend and meet Dutch breeders. There are always birds for sale.) Do you have the web address of the Dutch Bantam Club, with list of breeders?
www.dutchbantamclub.org
So, not to discourage you from enjoying your cross variety, very attractive cockerel (he does have a beautiful ear lobe, but a very poor comb) it would, perhaps, be good to locate a Lavender pullet or a Black pullet to go with him. Have seen on of the best Yellow Partridge cockerels-ever--in Scotland! Good luck.