There's a thread on here somewhere that we had talked about photo taking. Maybe someone saved the link and can post it or can find it and post it.
I use umbrellas when I take photos. Usually a black one for dark colored blooms and a white one for the others. Even if the sun is behind the clouds the umbrellas can help filter the light so the blooms show more true to what you see.
I have fooled around with my camera settings and I have found that the portrait setting with the macro on works best for me. I've tried several different settings and messing with the menu settings as well to get better red/purple coloring but it didn't seem to help. I had looked up my specific camera and problems and followed what was suggested.
I try and take my photos early morning, but I find if it's too early the color can be off. There is a big difference sometimes between a photo taken at 6:30 am and 7:30 am. It has to do with the natural lighting.