“how pelargonidin behaves in diploid vs. triploid vs. tetraploid”
Historically diploid polyanthas were by far the earlier pelargonidin source, see Orleans Rose sports and seedlings. Some were mesured very high in pelargonidin. Probably derived from multiflora Crimson Rambler.
I have a nice quite orange wichuraiana rambler from Immensee OP seeds. Very wich looking. A probable triploid.
Pierre, I realize that but that is not what I am asking. I am mostly curious about visible expression because the diploids were not delved into too deeply so we did not get to see the garish tones and fading bred out, if they can be. Coral Drift is as about as far as we have in terms of diploid + orange. Another factor is that foetida yellow may have strongly contributed to the expression of the visible orange we can see in roses such as Gingersnap. I am choosing Gingersnap as an example because everyone has seen it. Personally, I hate it 
So my question is not about the availability of pelargonidin in diploids vs. tetraploids. It is about the possibility of aesthetic and diverse expression to our eyes.
Mildew affects 'Floradora’s babies here, that’s for sure 
Of the youngins here now only two don’t have woolly coats. Interestingly, these are also the only two to have flowered with decent flowers. Another thing I’ve noticed with the OP babies so far is that ‘the apple doesn’t fall far from the tree’. These are the best two from the batch of OP ‘Floradora’ seeds germinated here:
This is the first one:
Not sure that I like this one much. The darker ‘smudges’ don’t do it for me and this one fades like you describe, Kim.
This is the second one. I like this one much better. Hasn’t faded like you describe Kim either. It just opened to this point and stopped changing altogether and then started to shrivel and die after a week or so on the plant… we’ve been having strange weather though… It’s growing outside in the sun as well.
I’ve given up trying to keep the mildew off the remaining seedlings… they will never amount to anything and will be binned when I get a little spare time.
I’ll keep these two on for a while longer and want to run these through ‘Trier’ because I love the HM form in the garden.
Looks rather like opinions that two decennies ago were common among daylilies breeders.
Even if so little investigated or bred for I do not think there is anything that could hinder pelargonidin expression and diversity of in lower ploidies.
I.e. Lens’ Lovania that has only one poor picture on HMF is from Robin Hood x (New Penny x Coloranja). Diploid as I grew it and as bright an orange-scarlet as any.
Color fastness is never given. Rosa species flowers are often operating for a single day and few last more than three.
My opinion is that if 1% of rose breeders energy were long enough dedicated to diploid improvement you could ask the opposite question.
Actual daylily breeders do no longer question that.
Flower Carpet Sunshine (Yellow) is triploid and fertile. Add it to the short list of random yellow triploids created over the decades, I guess. I believe it works both ways but this is not out of personal experience. I find the color to be somewhat fleeting but okay for a yellow groundcover where most are barely even primrose toned.
It seems almost worthwhile to attempt to create a yellow diploid stud (or studette!) for breeding purposes only. Easier said than done, Im positive.
‘Flower Carpet Yellow’ has only been fertile as a pollen parent here with tetraploids… haven’t tried it with diploids. I assumed it was because it was producing 2n pollen. I’ve never seen a hip on it here in four years. Used it tonight as a pollen parent with ‘Wild Rover’ that is dark purple but whose OP (selfed) progeny are purple/yellow blends. Bernhard has used ‘Flower Carpet Yellow’ to great effect with ‘Sympathie’. I have a feeling all the flower carpets are triploid aren’t they? ‘Flower Carpet Amber’ set enormous quantities of OP hips for me last season and I haven’t been able to get a single one to germinate… can’t be a good sign . Used its pollen tonight as well on ‘Wild Rover’ to try it as the Dad this time.