Apple AppleVision monitors (OS 7.1) - Manual (Page 49)

Adjusting convergence
Red, green, and blue signals in your monitor intersect, or converge, to create
the colors you see on your screen. If the convergence is not set properly,
images or text on your screen may appear blurred, or you may get a
“rainbow” effect in which several colors form the edges of images on
the screen.
Also, over time the convergence may need to be adjusted to maintain a clear,
distinct screen image.
To adjust convergence, follow these steps:
1 Open the Monitors & Sound control panel, then click the Geometry button.
2 Click the Convergence button.
The convergence screen appears.
49 Geometry Settings
Click to adjust
convergence.