Mpbp, there are probably several ways to do it.
I would save my original file and name it 4C-cmyk.
Save that file again and name it as BW and change it to B&W. Under file-change it to duotone. Pick out the brown that you want and save it in duotone.
Change that duotone file to cmyk.
Add a new layer as multiply.
Go to the original and do a path for the color area. Copy that and paste onto the new layer. Position the new layer to cover the cmyk duotone image and if everything looks good go to layers and flatten the image.
Now you will have only one layer.
Save it as CMYK or JPEG.
Duotone backround with a 4-Color flower image.
Have fun doing it.
I have a digital picture that I would like to print in sepia but with a bouquet of flowers in color. How do I do this? Thanks