Ian,
basically it's buff columbian X mottled/spangled X lavender
so yes it's a lavender mille fleur.
It's way easier to just type it down to do this and that and your there, but the real world, creating a new color in a breed is far from that simple. Every little cross which is so quick to type out is a full year of your time, then you have to mark each bird so you know what it carries, raise that bird to breeder age, then cross it again, and repeat. Here's the full detailed plan for what you are after.
lavender is recessive ( as is mottling) so when you breed a mille to a lavender bird you arent going to get anything but black right off
you'll have to back breed these black chicks to get both the mottled and the lavender to come back out, plus you'll have to get the buff columbian pattern back too.
There will be tons of culling as you will get mostly the following (rmember this is year 2 already) Good thing is, all these will be true colors if you wanted to work with each of them later on.
solid black
black mottled
solid lavender
lavender mottled
then you will also get
buff columbian
milles
lavender columbian
porcelains
bb red
and spangled
the lavender bb red
and lavender spangled
Being that you'll be working with 2 recessive genes here, all those will come in split versions too, some will be split for lavender and mottled, some of the lavender will be split for mottled, some of the mottled will be split for lavender and so on...
It's not going to be an easy quick deal, especially if you are working with a very limited supply of birds just due to all the variables and 2 recessive genes, it makes for tons of possible out comes. Plus at this phase, you will have no idea who is split for what and how is just what is is expressing visually.
A quicker route for the COLOR would be a mille crossed to a porcelain. you'd get all milles the first time, they would all be split for lavender, back cross those and you'll have you porcelains...NOW the problem is puring up the type though. Once again, lavender being recessive will make each cross back a 2 year process to help pure up the color. Cross you new 50% pure porcelains back to the original mille bird, and repeat the above process for the color again...
Either way you go, it can take several years. God luck to you on it.