From the source:
 
“Because I love their designs <3  
Also this would be a good time to provide my headcanons.  
Spoilers obviously.”
 
“First up, Sour Sweet. Now first I want to diagnose her with maybe hypomania, it seems as though she does have a bipolar disorder. Anyway, I can see her talent being something relating to her heart. Sour Sweet’s talent was actually the hardest for me to come up with something, but I think I understand it now. A heart within a heart, but with a diamond? Well, diamond’s are a symbol of prosperity, and heart’s symbolize love or passion. I would say Sour Sweet’s talent is helping others in general, sort of like a counselor. She already battles with herself to keep her emotions at bay, and so with her knowledge, she can probably carry it down to others who need guidance.”
 
“Sunny Flare. Her design is actually my favorite. Now to her talent. I didn’t quite understand why she has a sun and a rain cloud, but it could be metaphorical. They’re in colors associated with herself, so I would assume they pretty much are metaphorical. Now what else do we notice about her though? Her mane. Notice how she’s the only one with a cut in the movie, like she possibly cut her hair herself. Also, what I did was derive her name, flare. Flare means bright, but flair means: with style. Basically, Sunny Flare’s talent is coming up with bright ideas that she keeps to herself. As in, she has her own styles or inspirations that she hides behind her gloomy attitude.”
 
“Lemon Zest. Her cutie mark confused me a bit. I assumed it was like lemony zesty stuff or something, but then I read they were fireworks? I dunno, but then I looked at her headphones; they have a slice of pie on either side. I want to pretty much say that her talent involves sweets, maybe preparing pies like a lemon meringue pie. However, not just sweets, but savory flavors too. Lemon Zest’s talent is mixing her own things together to make something new.”
 
“Sugarcoat. Her cutie mark didn’t make sense to me either, just like Sour Sweet’s. I would even say their cutie mark’s should be switched, but eh oh well. So her cutie mark is a stick of dynamite; I wouldn’t have seen that coming. But, what does dynamite do? It causes a reaction. I would say, Sugarcoat’s talent is causing a reaction, since she’s blunt all the time. Initially, she could’ve been negative to anyone, but I think after the Friendship Games, she learns to cause positive reactions instead, like complimenting someone.”
 
“Finally, Indigo Zap. She was the easiest for me, since well she’s pretty much Rainbow Dash. I mean come on even their names are similar: Rainbow Dash, Indigo Zap. Anyway, if Dash’s talent is flying fast, then I would say Zap’s talent is the same… but that’s boring. I do notice that her cloud is dark, so that leads me to another conclusion: Indigo Zap’s talent is flying recklessly.”