"The orange soda pop is sweet."
Translation:Oranssi limonadi on makeaa.
My take on this, but be warned that I'm still learning the subtilties of partitive:
The "orange soda" is the subject in this sentence, we're talking about this soda in particular, as if it's in a bottle we're pointing at, or as if we're talking about a specific kind of soda. So the whole subject group adopts the nominative case. However since "limonadi" is still an uncountable noun the adjective following the verb has to adopt the partitive case.
If a native or admin comes over here, do tell me of my explanation is off.
It's easy to confuse oranssi (orange color) and appelsiini (orange fruit) for English speakers. People will figure out what you mean if you order "oranssi mehua" (orange colored juice) in a restaurant, but you'll get really weird looks. Not that I would know this from experience or anything. <.