Select all pixels of one color in ImageJ

I want to develop a plugIn for ImageJ that clicking over a pixel (of a determined color) it selects all the pixels of that color and the rest of the image in black (except if the selected pixel is black).

I coded the next:

import ij.ImagePlus;
import ij.gui.ImageCanvas;
import ij.gui.ImageWindow;
import ij.plugin.filter.PlugInFilter;
import ij.process.ImageProcessor;

import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;

public class PlugInMouse_ implements PlugInFilter, MouseListener {
    ImagePlus imp;
    ImagePlus ni;
    ImageCanvas canvas;

    @Override
    public int setup(String arg, ImagePlus imp) {
        this.imp = imp;
        return DOES_RGB + DOES_STACKS + SUPPORTS_MASKING;
    }

    @Override
    public void run(ImageProcessor ip) {
        ni = new ImagePlus();
        ImageWindow win = imp.getWindow();
        canvas = win.getCanvas();
        canvas.addMouseListener(this);
    }

    @Override
    public void mouseClicked(MouseEvent arg0) {
        int x = arg0.getLocationOnScreen().x; // seleciona a posição do clique
        int y = arg0.getLocationOnScreen().y;
        setDrawingColor(x, y, false);
    }

    public void setDrawingColor(int x1, int y1, boolean setBackground) {
        int bi = imp.getBufferedImage().getRGB(x1, y1);
        for (int corte = 1; corte <= imp.getNSlices(); corte++) {
            int[] pix = (int[]) imp.getStack().getProcessor(corte).getPixels();
            for (int i = 0; i < imp.getWidth() * imp.getHeight(); i++) {
                if (pix[i] != bi & pix[i] != 0x000000) {
                    pix[i] = 0x000000;
                }else{
                    pix[i]=pix[i];
                }
            }
        }
        imp.updateAndDraw();
    }

    @Override
    public void mouseReleased(MouseEvent arg0) {
    }

    @Override
    public void mouseEntered(MouseEvent arg0) {
    }

    @Override
    public void mouseExited(MouseEvent arg0) {
    }

    @Override
    public void mousePressed(MouseEvent arg0) {
    }
}

The thing is: It works pretty well except that it draws a kind of a box outside the color and it doesn't always work. Sometimes I click over a black box and it puts all the other boxes black.

Can you help me?