As you can clearly see, no trivial shader effects / rectangles / circles can accomplish this.
Images / Bitmaps are used.

So simply repeatedly draw Bitmaps using canvas.drawBitmap. You draw the same Bitmap again and again while the finger moves.

For adding a custom color you can add a simple filter.

An Example

public class CanvasBrushDrawing extends View {
    private Bitmap mBitmapBrush;
    private Vector2 mBitmapBrushDimensions;

    private List<Vector2> mPositions = new ArrayList<Vector2>(100);

    private static final class Vector2 {
        public Vector2(float x, float y) {
            this.x = x;
            this.y = y;
        }

        public final float x;
        public final float y;
    }

    public CanvasBrushDrawing(Context context) {
        super(context);

// load your brush here
        mBitmapBrush = BitmapFactory.decodeResource(context.getResources(), R.drawable.splatter_brush);
        mBitmapBrushDimensions = new Vector2(mBitmapBrush.getWidth(), mBitmapBrush.getHeight());

        setBackgroundColor(0xffffffff);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        for (Vector2 pos : mPositions) {
            canvas.drawBitmap(mBitmapBrush, pos.x, pos.y, null);
        }
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {

        int action = event.getAction();
        switch (action) {
        case MotionEvent.ACTION_MOVE:
            final float posX = event.getX();
            final float posY = event.getY();
            mPositions.add(new Vector2(posX - mBitmapBrushDimensions.x / 2, posY - mBitmapBrushDimensions.y / 2));
            invalidate();
        }

        return true;
    }
}