Weird, I checked the console and it said "Colorset: 449"
Or somewhere around that number
Looked into it more. One color actually takes up seven datablocks.
So 64 x 7 = 448.
Here's the breakdown of the datablocks.
Explosion Emitter > Explosion Particle
Image > Projectile > Explosion >
Explosion Droplet Emitter > Explosion Droplet Particle