Denny,
I went through this a few years ago and finally came across a reference for it in a column in the VCCA mag from the AD tech rep, ( I think you'll know who I mean.) He had cross referenced it to a 1977 Subaru

white called Plaza White. I don't have the can here with me so I can't get the number off hand. It's a fairly stark white, sort of like milk. It matched real well to the original white on my '50 and the traces of white still on the '51 grill. If I remember correctly, you didn't disassemble your grill to reveal any white behind the outer bars.
And no, I haven't finished the '51 yet. I really have to get going on it again, I can't seem to find time for it right now.
Bob