Hi Alex,
Can't say that I'm a huge fan of selective colouring in most circumstances and TBH it's not really working for me in the image here.
However, if you set out on this as an exercise in PP to practice the technique I think you've done well - and it's all part of the learning curve. Once you've mastered how to do it, learning when to use it to best effect is the next step.
The other thing to think about to move up to the next level is the quality of the B&W conversion and getting some nice contrast and tonal range into it.
In terms of the image as a whole, I think I would have really liked to have seen a bit more of the memorial to give some context of where you shot it.
We can see a bit of the stone at the bottom right of the picture, but it's neither really here nor there. It's dominant enough to draw your eye towards it, but it's not really clear what it is so it becomes a distraction rather than a part of the image.
