Selecting Breeder Queens, yellow or dark?

I am primarily trying to breed dark, near native bees and have managed to make reasonable progress although most colonies have some workers with yellow banded abdomens. Considering I'm based in Cheshire which has a large number of beekeepers, many of which purchase Buckfast bees, this isn't a great surprise.

Dark, local bees, these were sold to a gent that I was mentoring a few seasons ago. They were very docile and produced a honey surplus in their first year.

I have over the last five years bred as many queens as I was able to with the equipment I had available, trying different methods of queen rearing, selecting desirable stock and culling the least desirable.

A Buckfast swarm caught just a mile from my apiary

However, I have a yellow queen (she's marked yellow too, 2017) that has provided me with brood frames and bees to make up a large number of nucs, bees for Apideas and produced a honey crop each year that has surpassed all of my other colonies. In addition the colony is very calm on the comb, the bees just don't seem to realize that they are being scrutinized. As far as I recall I have had no stings from this colony either BUT they are (the workers) 40% yellow. Last year and this I had ear marked her as "break up into nucs" but she (the queen) just keeps on giving, what to do ......

Nucleus colonies ready to go

This spring, feeling that I should repay the dept, I deciding to graft from this very productive and un-swarmy queen. I didn't want to use up a lot of resources so I chose to use the remains of a strong colony on double BB from which I had taken a nuc from to donate to my association apiary as a cell raiser. I put in seven grafts, four of which took and subsequently went on to produce laying queens. The last of these went on to their new owners today, these last two were on four frames last Friday in a "Twinstock type" nuc double from cornishhoney.co.uk. When I transferred them into their sales nucs on Sunday they had built the fifth frame out and the queens had laid in them. They were all as calm on the frame as their mother's colony, hopefully they will continue to be so as they expand and grow with their new keepers.

A twist in the tail:
This colony, having been a dream to work with is currently on a double BB with five supers, finally decided to let me down: I inspected them this Sunday, There were a couple of sealed swarm cells and more unsealed, luckily my yellow queen had been clipped and was still resident. She was easily transferred to a nucleus along with another emerging brood frame plus bees (WITH NO QUEEN CELLS: this is important!!) and a frame of stores. She will hopefully come back into lay and build up up the strength of the new colony.

So what to do now? We are told to "go with the bees". So my plan is to use the now queen less colony as a cell raiser in two cycles, one to raise more queens from one of my Irish queens, transferring them to cell finishers and then raising more queens from this industrious yellow queen.

The original colony obviously have their minds set on raising queen cells, so I will set them up and let them do their thing: Rear queens! I'll overwinter the resulting queens as nucs, using them in the spring to replace winter losses, nuc building or, if the winter is kind, sell any surplus in the spring.

I'll post some more pics here as we go through this process.