Hes a boy for gosh sakes the blue would make the star pop
My choice is blue however orange would be second but definitely blue try both and see let me know what you end up with
Your star has blue,green or orange I would go with one of those colors , It will be the love that you put in it that counts anyway. I am sure your grandson will charish it .
A friend of mine used the black music notes in a windmill and she used the orange- lime grn and yellow for sashings and it is -----Like really cool-her GS loves it