Having only one colour in an image can be a little limiting.
In the original image the badges on the tank are Red as are some of the reflectors. Using the medicine dropper to identifies that they are located in the red zones at either end of the hue range. A small modification to the histogram results in the following image, not perfect but worthy of further investigation. To restrict the effects of the conversion to green I reduced the range of colours mapped to green and added anchors to prevent the reds moving into the colours between red and green. If you try this, leave the anchors until last, then when you add them you will clearly see where the reds were mapped to before the addition of the anchors. Anchors (single ones in this case) are frequently necessary to limit the effects of radical colour changes.