Thanks to all for your help! @Eugenia, I'll check out your book!

I've been doing freezer jam and the flavor stays intense as does the color. There is a specific pectin to use for freezer jam. Packing in small batches I pull out anytime over the following year as wanted. I also find I use less sugar, although with rhubarb stick with the recommended amount until you figure out your own taste level.

I've also noticed that my strawberry jams seem to darken relatively quickly, even when kept in a cool, dark, spot. I honestly don't know if it is the rhubarb or the strawberries but suspect either way it has something to do with the skins. I also make rhubarb jelly and strawberry jelly from essentially the same fruit sources and those retain their beautiful colors much better. I don't know if you used pectin, but when I do, those jams/jellies also seem to retain color better.

Hi: Green-fleshed rhubarb with red skin will cook up brown. Red-fleshed rhubarb with red skin will cook up red. Note there may be some oxidation in your jars regardless of which rhubarb cultivar you use.