Summoning a firework with a custom color always appears black

The bug

When I discovered that selectors stopped breaking, i hopped into a minecraft world to tinker a bit with fireworks and commands. When I tried to summon a fireworks_rocket with custom NBT tags to make it have different colors, it always appeared black.

Steps to reproduce

1. Go to a minecraft world in 1.12-pre5. (Make sure the world has cheats enabled.)
2. Use this command:

   /summon fireworks_rocket ~5 ~ ~ {LifeTime:0,FireworksItem:{id:fireworks,Count:1,tag:{Fireworks:{Explosions:[{Type:1,Flicker:0,Trail:1,Colors:[0,16777215,14408448],FadeColors:[8026746]}]}}}}
   

   • The firework is supposed to have custom colors, but it doesn't.
3. Close Minecraft, and open version 1.11.2
4. Go to a world in this version
5. Use the command as described in point 2.
   • The firework does have custom colors.