Q:

How can I know what an enemy team's strongest color is? 

In Marvel Puzzle Quest, the 'Surgical Strike' skill of Wolverine (X-Force), destroys all tiles of the enemy team's strongest color, doing damage per tile. 
I know from experience that it is not the color with the highest AP count, so what is the deciding factor ? 
The level of the character currently in front ?   The most powerful skill of that character ?   The 'primary color' of a character ... ? 
Update: Blade (Daywalker)'s 'Nightstalker' skill also influences the enemy's strongest color. 

A:

For a single character his strongest color is the one in which he has the highest match damage: for example Thor(Modern) deals 79 match damages with red, 70 with yellow and 61 with green, so red is his strongest color. 
In terms of team composition you simply add up the match damage of the three characters in every color and the highest one will be the team' strongest color.  This means that, when you down an enemy, the strongest color changes because it factors only the characters still capable of fighting, so Surgical Strike played in different moments of the match could destroy/drain different tiles.