He probably doesn't want a saddle pad for his birthday why don't you get him some treats or a jolly ball
Blue or teal! and treats are always a good present☺️
I would say that your horse's color would go great with a teal or blueish color
I love hunter green and aqua blue on greys. Also, a deep greyish purple matches a grey very well. I also like getting not just saddle pads but new tack like boots, a new halter, or a new bridle. Get him his favorite treat and spend a lot of time with him. If your barn has a trail, go on trail rides with him and do all his favorite activities. I hope your pony gets to enjoy his birthday!
Any vivid colours like aqua, hot pink, orange and purple will look great on a grey of any kind
Hope that helps😉