" How likely is it that the RR plants will consistently have less red pigment in their foliage than the Rg and gR plants? "

If simple Mendelian genetics actually applied to your cannas, there would either be red pigment, or no red pigment, so the question of less red or more red would not apply. However, there is no reason to assume that Canna foliage color is controlled by a single gene. And Mendelian genetics is an old pre-DNA theory. Genetics has come a long way since Mendel.

" I ask this question because, based on percentages, that seems to be the case with my canna Intrigue seedlings... "

A sample size of 22 plants isn't large enough to establish percentages. It seems likely that your Canna foliage color is governed by more than a single gene.Your picture of Canna seedlings does suggest genetics questions. Good picture.

ZM

Note, 4/22 of the plants are light red, 6/22 are green and 12/22 are dark red, which is consistent with my hypothesis. Also, consistent with my hypothesis is that Canna Intrigue, is apparently gR rather than RR. Why would whoever bred Intrigue select a gR over an RR, unless gR were redder than RR? If RR were as red as gR, you would breed RR plants to get the desired result instead of wasting time on 25% green plants.

Anyway. this can be resolved by examining self crossed offspring of the light red plants. If my hypothesis is correct, all of the offspring will be light red like the parents. But, then what? The light red plants have no commercial value. I can't even use that knowledge to win a bar bet. It's too much work to just satisfy my curiosity.

Canna Intrigue is apparently gR rather than RR. Why would whoever bred
Intrigue select a gR over an RR, unless gR were redder than RR?

Warning:

I don't know what I am talking about.

But could it be because gR plants are stronger?

In budgerigars, which I bred way back when, their is a pattern called Harlequin. It is very striking. And it's recessive. So all you need are two Harlequins and you're laughing.

Except... if you breed harlequins with other Harlequins, your birds will become small and weak. I was warned of this so I never did it. I would partner a Harlequin with what is called a split, which is half a Harlequin. Being a recessive gene, it doesn't look like a Harlequin. You only know the fact because you know its parentage. (It is probably better still to breed a split to another split.)

Could the same be so for Cannas? You are better off breeding gR to gR even though you get roughly only 25% dark red. At least those dark red ones will be healthy and vigorous.

"But could it be because gR plants are stronger?"

I don't know about gR versus RR because I am uncertain of the identities, but, the green plants are growing at least as fast as red leaved plants. But, it seems that red pigments generally do not improve photosynthesis, if not hinder it, because otherwise, most plants would be reddish as a result of Darwinian evolution.

Incidentally, I have been told that the flowers of all green leaved offspring will be yellow and flowers of all red leaved offspring will be pastel orange. I expect my plants to flower in August.

Anthocyanin pigmented plants darkness are often red or purple dependant on intense sunlight and cold temperatures but not always. Its possible the dark red ones you are observing are actually because chlorophil may make them seem a darker red even though you cant see the green (Rg). Anthocyanin in some ways can replace chlorophil as the plant uses different pathways to produce sugars from the sun. Anthocyanin is more advantagous at cold temperature where chlorophil is not able to function. Chlorophil however is more efficient and is overall better. But plants that can do both are at an advantage over those that only have one or the other.

"Anthocyanin is more advantagous at cold temperature where chlorophil is not able to function. "

That would certainly be useful information, if true, but I doubt it because the proportion of red leaved plants in cold climates is not substantially different than the proportion in warm climates. In fact, some of the most outstanding red leaved plants, e.g., cordyline terminalis, are tropical. See https://www.google.com/search?q=%22cordyline+terminalis%22&rls=com.microsoft:en-US:IE-Address&biw=1280&bih=641&source=lnms&tbm=isch&sa=X&ved=0ahUKEwixicCv4N7MAhUm_IMKHY_PCN8Q_AUIBigB

And, cold or warm climates, the vast majority of red leaved plants exist only because of human interference with nature for ornamental purposes. It occurs to me that an exception might be algae, but, algae is generally too strange to consider in the current context.

Anthocyanins are only present in extreme sunlight unless "hard coded" to be on all the time. You will find examples of both if you grow enough. But anthocyanins are able to convert sunlight to sugars at colder temperatures than chlorophyll, they are just not as efficient as chlorophyll, so overall chlorophyll has a greater advantage and therefore a bigger presence in biology. But the plants that can take the greatest degree of cold stress will always have anthocyanins compared to those that do not.

"But the plants that can take the greatest degree of cold stress will always have anthocyanins compared to those that do not."

Name one that is not algae.

Corn (from my own garden). Mine survive multiple frosts in April. They are very frost and snow tolerant. I live at high elevation, so i get more intense sunlight, so perhaps they do better for me than they would in other climates. They probably would not grow as well in climates like Africa for example and genetically would naturally be selected out of a population.

But going back to your original question even with my corn, generally the ones that are heterozygous for the purple foliage do better than either the fully green or the darkest purple corn plants. One might argue that could be because of Hybrid Vigour, but in my experience that's not the complete answer as many of mine are genetically related to each other.

1. That is not very red or purple.

2. The ability of herbaceous plants to survive frost is completely dependent on the amounts and types of solutes that are in a plant's sap that depress the freezing point thereby preventing ice crystals from rupturing cell walls.

This particular photo was taken mid summer with heavy heat ans as such the anthocyanin levels are lower that they were earlier in the plants life. I've had plants with 100% purple and no green visible before. And while you are partially correct in your second statement it is not completely dependent on that. There are many other chemicals which play a role in such cases such as flavonoids and anthocyanins. You are free to your own opinion, but it seems strange to ask questions about things that you already have made your mind up on. I will end on that note and bid you good day. Hope you find the answers you are looking for.

http://www.ncbi.nlm.nih.gov/pubmed/25504198

http://onlinelibrary.wiley.com/doi/10.1111/j.1751-1097.1999.tb01944.x/abstract

http://www.plantstress.com/articles/up_cold_files/Cold%20acclimation%202010.pdf

Thank you for the references, but, most evidence suggests that increased anthocyanin synthesis is sometimes an effect of cold exposure rather than the cause of cold tolerance. Note:

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Decades ago, Parker (30) linked anthocyanin appearance and disappearance to cold hardiness in Hedera helix leaves. Further work (I 16) refuted these results, demonstrating no correlation between hardiness and anthocyanin levels in H.helix. It should be noted, however, that these latter experi- ments were conducted in a greenhouse and herefore the re- sults might not be indicative of field conditions (i.e. natural UVB levels). Parker (30), on the other hand, used field- grown leaf tissues. More recently, Singh et al. (7) studied anthocyanin content and its relevance to cold hardiness of field-grown chick- pea (Cicer arietinum). They concluded there was no association between stem anthocyanins and cold hardiness but did not report these data in the article. Furthermore, because this was not a controlled experiment zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA (e.g.outdoor temperature fluctuations), they would not be able to assess small, but significant, differences in cold hardiness among genetic
lines.
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If anthocyanin was a cause of cold tolerance, it would cause cold tolerance in every plant in which it is present, e.g., my red Canna Intrigue seedlings. I am going to leave both red and green canna seedlings in my zone 5 ground this winter. Do you want to bet that the red ones will survive longer? I bet that both red and green die on the first day that temperatures dip below 32 deg. F..