This page explains how the Field Effect works in Chrono Cross: The Radical Dreamers Edition.
The Field Effect is a constantly changing bonus/penalty that applies to everyone on the battlefield. It appears at the top-left corner.
What Determines the Field Effect?
The Field Effect always has 3 colors. At the start of battle, these colors are randomly chosen. For example, they could be: Yellow, Black, Blue.
Each time an Element is used (either by you or an enemy), the color of that Element will be added to the rightmost position of the Field Effect, while the remaining colors will shift to the left. Since the Field Effect only has space for 3 colors, the previous leftmost color will disappear.
Continuing from our example, if you or a foe uses Diminish (Black), the Field Effect will become Black, Blue, Black.
As the battle goes on, if many Elements are flying around, you can expect the Field Effect to keep changing.
What Does the Field Effect Do?
Do you remember the relationship between Elements?
To recap, Red and Blue oppose each other. Likewise with Green and Yellow and same with Black and White.
When an Element is used, for each color within the Field Effect that matches the Element’s color, the Element’s power will be boosted by 12.5%.
Eg. if the Field Effect is all Red, the power of Red Elements will be boosted by 37.5%.
Conversely, for each color within the Field Effect that’s the opposite of the Element’s color, the Element’s power will be reduced by 12.5%. This damage reduction is capped at 33.5%.
Eg. if the Field Effect is all Red, the power of Blue Elements will be reduced by 33.5%.
Therefore, if plan your Element usage well, you can manipulate the Field Effect to maximize your damage and/or minimize the foe’s damage. For instance, before unleashing a devastating Volcano (Red), you could spam Tablets (Red) to make the Field Effect all Red.
One more thing: There are certain Summon Elements that can only be used when the Field Effect is completely one color.