Double strong color, no weak color, teams==
Now that you have two rainbow teams ( one 3* 3.50 and one 4* 3.60 ) you can create double strong color, no weak color teams.
If you are attacking a Green Boss, then Red heroes are better because they are strong against green, so Green bosses takes double damage. The opposite is true of Blue heroes. Blue heroes cause half damage to a Green boss. The other colors ( Green, Purple & Yellow ) do neutral damage or no increase or decrease in damage.
When attacking a Green boss, remove your BLUE 4* 3.60 hero ( half damage against Green ) from your rainbow 4* 3.60 team, and replace it with your RED 3* 3.50 hero ( double damage against Green ) for a double red, no blue team.
You will do 1 HP of damage with blue matches/ board damage, since you are missing a Blue hero. But your two Red heroes will do double damage. Even if your Red 3* 3.50 hero dies against a Green boss, twice its attack stat will still be added when doing matching/ board/ physical damage.
==Weird color teams==
triple strong color,
quadruple strong color,
double neutral color,
double neutral three color teams and
single color teams.
Once you have more experience with rainbow teams and double strong color, no weak color teams, you can learn more about these weird alternatives.
==Elemental shields or Reflect color enemies==
When you fight an enemy with an elemental shield, it is weak to a color, strong to a color and REFLECTS a color. Example: A Reflect green boss takes double damage from Red heroes, half damage from Blue heroes, and reflects all damage from Green heroes back to that hero. So a triple red, no blue, no green team OR a double red, double yellow/ double purple, no blue no green team works better than a rainbow team. Example you can remove your Blue 4* 3.60 and Green 4* 3.60 heroes and replace them with one Red 3* 3.50 hero and one Purple/ Yellow 3* 3.50 hero.
So having a rainbow 3* 3.50 and a rainbow 4* 3.60 lets you take on Reflect color enemies until you level up a second rainbow 3* 3.50, second rainbow 4* 3.60, etc.