How do i make the ROI transparent?

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matlab l=Lng.PNG

I have a code that generates random ROIs within the left and right lung Boundaries. The code displays the ROI as a white box on the Lung. Ive tried to make it so the background image is still showing with the ROI superimposed on the image but can not seem to get it.

Any help on how to display the ROI as a box (that is not filled in) would be a great help

   %randomly select roi
    roi_size = 16;
    slice_list(i-first_slice+1) = i;
    roiCenters_left = zeros(numROIsPerSlice,2)-roi_size;
    roiCenters_right = zeros(numROIsPerSlice,2)-roi_size;
    for m=1:numROIsPerSlice
        [ left_roi_center_x, left_roi_center_y ] = chooseRandomROI( leftLung_binary, roi_size, roiCenters_left, numROIsPerSlice );
        left_roi = drawROI(leftLung_gl, left_roi_center_x, left_roi_center_y, roi_size);
        [ right_roi_center_x, right_roi_center_y ] = chooseRandomROI( rightLung_binary, roi_size, roiCenters_right, numROIsPerSlice );
        right_roi = drawROI(rightLung_gl, right_roi_center_x, right_roi_center_y, roi_size);