def METHOD_NAME(mask, color='lightgreen', alpha=1.0):
    """Convert boolean mask to RGB image object for canvas overlay.
    Parameters
    ----------
    mask : ndarray
        Boolean mask to overlay. 2D image only.
    color : str
        Color name accepted by Ginga.
    alpha : float
        Opacity. Unmasked data are always transparent.
    Returns
    -------
    rgbobj : RGBImage
        RGB image for canvas Image object.
    Raises
    ------
    ValueError
        Invalid mask dimension.
    """
    mask = np.asarray(mask)
    if mask.ndim != 2:
        raise ValueError('ndim={0} is not supported'.format(mask.ndim))
    ht, wd = mask.shape
    r, g, b = colors.lookup_color(color)
    rgbobj = RGBImage(data_np=np.zeros((ht, wd, 4), dtype=np.uint8))
    rc = rgbobj.get_slice('R')
    gc = rgbobj.get_slice('G')
    bc = rgbobj.get_slice('B')
    ac = rgbobj.get_slice('A')
    ac[:] = 0  # Transparent background
    rc[mask] = int(r * 255)
    gc[mask] = int(g * 255)
    bc[mask] = int(b * 255)
    ac[mask] = int(alpha * 255)
    # For debugging
    #rgbobj.save_as_file('ztmp_rgbobj.png')
    return rgbobj