I personally don't think there is enough of a difference between the cross and background to make selective colouring work in this interest. A nice high contrast B&W would be superb though
Nice original shot though and I can see where you were heading with it
B+W version is better. The cross doesn't have much colour in it anyway so its barely noticable as selective colouring.
One thing I notice is that you've got quite big areas of blown highlights and lost shadow in the picture. Don't know if that's down to the processing or just due to the very harsh lighting.