Adobe photoshop layers?

Question

I have a colorized picture of a rose. I want to to change the picture so that the rose and stem are still in red and green and the background is in black and white. How do i do this? I think i need to use layers

Answer 1

Create a new adjustment layer... Hue/Saturation... then on the layer mask paint the part of the rose with Black...

Answer 2

Select the rose and stem using the magnetic lasso tool. When the selection is complete, go to Select menu and click on Inverse. In this way all is selected but the rose and stem.
Now click on Image > Adjustments > Desaturate.
About the use of the magnetic lasso you can read this tutorial:

http://graphicssoft.about.com/od/photoshop/l/blrbps_3aleaf.htm