The two most difficult colors to photograph are blue and white. digital cameras will always inject some red into blue plants. to get the most accurate blue, you must use your graphic program to eliminate the red.
as for the white, most difficult. you must underexpose by at least 1 + 1/2 stops. white fools the cameras exposure meter and automatically sets the camera to over expose. if you use a polarizer to eliminate the water glare, it must be a circular polarizer for a digital camera.
now on the camera settings, use manual if you are familiar with it or set the camera to aperture priority. set the aperture as high as it can go and still give you a fast enough shutter speed as to not cause blur. a f-stop of f-11 or greater will give you most depth of field and hence a sharper image
have i confused you?
lou