Focus at infinity, and smaller aperture will accentuate dust.
The smaller the aperture, the pronounced the dirt. This holds true even in the studio when you're shooting tabletop a couple of feet away.
As for colour, if the dust was green then it would not show against the flowers. Haven't seen the colour of the dust as an issue before, but never discount a possibility.
Surely the colour would make no difference, unless it were translucent dust (sounds like something from the sixties). It just sits there and casts a shadow whatever the colour.
Mike -- Mouse in the House, London http://www.mouseinthehouse.co.uk =============================================================== GO TO http://www.prodig.org for ~ GUIDELINES ~ un/SUBSCRIBING ~ ITEMS for SALE
