That's great guys, thank you for the reply's, I will be getting out after the weekend for some people/urban/street stuff so I will be having a go. I suppose that's the beauty of digital, you have got so many options at your fingertips.
Here's a simple (but real life) example. A red rose with green leaves, and converted to greyscale in Photoshop.
And using the colour version more intelligently to take account of the colours, we have a simulated green and a simulated red filter to separate the tones of flower and leaf.