For the definite, you only use "svarta" if it comes before the noun:
Paraplyet är svart.
Det svarta paraplyet.
I have a question about attributive adjectives. I figured that I would get a Swedish-language book, so that once I knew a fair amount of Swedish I could use the book to practice. I'm a big Harry Potter fan, so I got Harry Potter och De Vises Sten. Why is de used instead of den, and why is sten used instead of stenen?
It's plural – de vise is an old plural form that is used in this set expression, but isn't really used outside special expressions like that. (btw it's an adjective that stands on its own)
And the reason it's sten is that we never have the definite form after possessives, neither do you in English. You wouldn't say the philosopher's the stone.
It's a so called nominalized adjective – vis is an adjective, but en vis functions as a noun. You have something similar in English when you say She gives to the poor. 'the poor' stands on its own so that the adjective functions as a noun.
The forms are: singular: en vis, den vise, plural visa, de visa or with the old form vise, de vise.
So I noticed that out of all the colours I know in Swedish (not that many, but most follow the rules), that svart doesn't have a double-t form for ett verbs. One thing I have noticed, though, is that it can be pronounced with either a long "a" or short "a" sound. Does this happen to have anything to do with the gender of the object which the colour is describing?
"Svart" is always pronounced with a short "a" sound. Compare to "svar" = answer (noun), where "a" is long.
French 'parapluie' == 'paraplyet'
The incredible amount of French loanwords is making learning Swedish after French very easy. I'm curious if other Scandinavian/Nordic languages have invented rather than borrowed words for umbrella, avenue, furniture, etc.
So, is there no "native" Swedish word for an umbrella? (I appreciate that the English word is a borrowing also, although it has nothing to do with the rain).
Umbrella has no "native" name in many european languages. The funny thing is that they are quite diverse, but all seem to be rooted in Latin, Italian, Spanish or French. For example, Polish "parasol" means "against sun" in Spanish, but Spanish word for umbrella is "paraguas", which means "against water". There are names which mean "shade-making" or "for rain" or "for sun" in all the languages you can think of, but they all have French, Spanish or Italian roots.
Maybe "native" is the wrong word. I was thinking perhaps of something a little more "teutonic" like the German "Regenshirm" (which, BTW, isn't particularly French, Spanish or Italian)...