What is the coerulea color form in Phalaenopsis? I see a lot of comments these days about what is a coerulea and what is not a coerulea, and using being loosely determined by what other pigments are and are not being expressed. Ultimately I think we are looking at this incorrectly and we need to redefine what a coerulea form is.
In the genus Phalaenopsis, there are no blue pigments. There are a range of green, yellow, orange, magenta and violet pigments. It's the combination of these pigments that gives us the full range of colors that we see in Phalaenopsis. While coeruleas are sometimes referred to as "blue" Phalaenopsis, in reality they are a violet in color. But what actually makes them this violet color?
There are three different pigments in Phalaenopsis called Anthocyanins that produce the range of colors from light pink, magenta, purple, and violet. Yet only one of these three pigments gives us the violet "coerulea" color. We refer to that pigment as Anthocyanin C, the third Anthocyanin. When Anthocyanin A and/or B are also expressed in the flower, it is no longer a violet color and starts to go to more of a purple or very dark magenta. So a coerulea form is very simply, the absence of expression of Anthocyanin A and B in the flower with only Anthocyanin C present. Other pigments will always be present, even in what appears to be a completely white flower there will often be some green and/or yellow pigments. This process is a mutation in the pigment production pathway where Anthocyanin's A & B are turned off and in some cases completely deleted from the pathway.
So what I want to propose is that a coerulea form is strictly defined by the absence of Anthocyanin A and B and expression of Anthocyanin C. It does not matter if other pigments are present or not, and to what level of saturation they appear in the flower.
With that line of thinking some of the cultivars of P. tetraspis f. brunneola would actually be defined as coerulea. There are other hybrids that will appear peach to brown, that would also be defined as coerulea because the only Anthocyanin being expressed is Anthocyanin C.
For a hybridizer, I believe this distinction is very important. What we care about with coeruleas is simply, is there a mutation that is blocking Anthocyanin A and B and/or genetically there is only a pathway for Anthocyanin C? For example in the case of the tetraspis cultivars 'Sue's Coffee' and "Jia Ho Coffee'; the answer is yes, the Anthocyanin blocking mutation is present and only Anthocyanin C is present.
With that in mind and to further illustrate this concept, I would classify the following example cultivars as coerulea even though the flowers do not appear as the traditional violet coerulea color to the eye:
I have a longer article in progress attempting to further define the coerulea form and put in place some common terminology to help with describing the different coeruleas. But thought I would get this early/short description posted to gauge everyone's reaction.