it would be really difficult to match the grey colour with spray paint. it is not like the wall paint where you can ask the hardware store to match it for you.
My Trackmaster/Tomy/Plarail Photo Gallery Page (over 600+ photos and still under construction)
https://www.flickr.com/photos/183311600@N03/
https://www.flickr.com/photos/183311600@N03/