Has anyone seen or tried them?
There seem be different varieties.
According to this site, Cream of Saskatchewan are "very sweet and crisp and flavorful"
However the Citron watermelon is "is not your typical watermelon. The white solid flesh is inedible raw. It has been grown to make preserves and sweetmeats that are added to fruitcakes, cookies, and puddings. The best ones can be stored for up to a year. A variety that was widely grown on 1930's and 1940's"
Both those are green outside. In Costa Rica I saw some with a creamy white skin. Don't have a clue what the inside is like. Photo below.
I was prepared to forget about white watermelons until buying a normal melon in Guatemala yesterday. The guy I was with asked if I ever had a white watermelon. It seems someone grows them locally ... for export only ... otherwise I would have rushed down to give it a try myself.
Forget about citron melons unless you are big into candying. You can still get them from some of the old heirloom seed companies though. Basically they were used as follows, if you chop the flesh up and candy it or preserve it in syrup (possibly adding a little lemon peel) you can get a sort of "mock" verision of candied citron (actually the peel of a kind of citrus) for use in many bakes goods (Pannetone, Cannoli and Fruitcake are three that come to mind easily). A lot of the ones are the market are french, and usually have names that begin with "a confiture a graines" (something along the lines of "the confit maker with the ------seeds) the two most common seeds are rouge (red) or vert (green). There are also a few non-watermelon squashes used for similar purposes such as Pastela (a ficifolia squash used in the same manner in S. america, where citron melons don't like the climate) and Zucca/Sheepnose Melon, a kind of bottle gourd that at one time was used to make fake citron on an industrial scale (those bottles gan get well over 100lbs)
As for "real" white watermelons, it varies a bit. A lot of white fleshed watermelons are a bit low on the brix (the measure of thier sugars i.e. how sweet they taste). I grew two white types one yeat (C.S. white flesh and White Wonder, I recall) and while the resutlant fruits were certinly refereshing, they really tasted more like something I would put in a salad than serve for dessert, though when I juiced them, the resulting juice tasted like watermelon. Cream of Saskathewan is ok, but also a little balnd If you are willing to bite the bullet and try and grow them (probably the only way you experiance them, unless you live near a VERY big farmers market.) the white with the highest brix (and thefore the sweetest flesh) on the market I know of is probably a type called Japanese Cream Fleshed Sukiya. Baker Creek (www.rareseeds.com) has seeds for it, usually. There is also one called White Sugar Lump, but I haven't tested that one yet.