According to the spec, ColorModel.getRGB() could only throw
IllegalArgumentException "if pixel values for this ColorModel are not
conveniently representable as a single int". However, the following program
shows that ArrayIndexOutOfBoundsException is thrown from
IndexColorModel.getRGB():

import java.awt.*;
import java.awt.image.*;

public class IndexColorModelTest {
    public static void main(String[] args) {
        ColorModel cm = Toolkit.getDefaultToolkit().getColorModel();
        if (cm instanceof IndexColorModel) {
            int[] pixels = { 0, 1, -1, Integer.MAX_VALUE, Integer.MIN_VALUE,
                             50, 2467, 72693, -28, -892, -29023};
            for (int i = 0; i < pixels.length; i++) {
                try {
                    cm.getRGB(pixels[i]);
                } catch (ArrayIndexOutOfBoundsException e) {
                    System.out.println("ArrayIndexOutOfBoundsException thrown on " + pixels[i]);
                }
            }
        }
    }
}

output:

ArrayIndexOutOfBoundsException thrown on -1
ArrayIndexOutOfBoundsException thrown on 2147483647
ArrayIndexOutOfBoundsException thrown on -2147483648
ArrayIndexOutOfBoundsException thrown on 2467
ArrayIndexOutOfBoundsException thrown on 72693
ArrayIndexOutOfBoundsException thrown on -28
ArrayIndexOutOfBoundsException thrown on -892
ArrayIndexOutOfBoundsException thrown on -29023