Which are the tough to dye heads?

Most common tough plastic heads by manufacturer:

• ECD
  • Atom
  • DNA
  • Ion
  • Halo
  • Infinity Pro
  • Impact
  • Weapon X
• Gait
  • Mustang
• Maverick
  • Degree Series: This doesn't dye! Do not attempt
• String King
  • 2F
• STX
  • Prism
  • Duel 3
• Warrior
  • Burn XP2
  • Burn XPD
  • EVO QX2