This command works as expected in 1.11 but not in 17w16a. There are particles but now they are always grey.
/summon fireworks_rocket ~ ~1 ~ {LifeTime:11,FireworksItem:{id:fireworks,Count:1,tag:{Fireworks:{Explosions:[{Type:0,Colors:[16711680,3014403,16776963],FadeColors:[1666815,16727480,11927039]}]}}}}
New NBT parsing, you need to define the lists as int arrays like so:
Colors:[I;16711680,3014403,16776963]