This is a question about the use of color filters for B&W photography. I have a scene consisting of graffiti on a grey concrete bridge abutment surrounded by greenery. I have made a photograph without filters, and as I feared, there is virtually no tonal separation between the abutment and the surrounding greenery, the grey of the concrete photographs as the same shade of grey as the green leaves and bushes. (I have not posted the image, because the graffiti that attracted me is political, so some will enjoy the image, but others will be offended.) I have a reasonable number of color filters, but don't even know which to try (i.e. I can separate green and red, or blue and green, but am stymied by grey and green). Any suggestions?