OP, your horse is grey. 100%, no doubt or hesitations about it.
As for what colour he ends up, all greys will end up white eventually, some with flea bites and some without. The only thing that will change that is if the horse passes away before the greying process gets that far, as some horses grey really slowly. Looking at your horse, I don't think he will be a slow grey, I imagine he will be mostly white by the time he is 10 or 12.
When it comes to what colour he is under the grey, it is impossible to tell without seeing his foal coat - not after his first shed, but literally his newborn coat. It is not at all unusual for lighter colours to get a lot darker before they go lighter again, so that isn't a reliable way to tell what colour he is under the grey. This guy is palomino going grey, just to show what I mean about getting darker first. He will end up white too, just like any other grey.