It does seem to be a complex business, working this stuff out! I had a go using the Mutation and Colour Guide here: Cute Little Birdies Aviary - Welcome To Our Aviary! which is super informative! But I am still not totally sure, so I hope some more expert people can help out with the definitive answers as I'd be really interested to know
Thanks for the replies! That looks like a consensus for Petrie! I have looked up opaline markings for Alba, but it looks like he should have a V of his head colour extending down between the wings, but he does not. Does that mean he is not opaline? Also, his body is more blue (very pale) than grey of his wings. Does any of this change what people are thinking? I'll add another photo of Alba for extra ID possibilities!
Thanks again! There are so many combinations it is tricky but fun to work out what they are!
Thanks for your help Here's a photo of his back. I hope this is ok, I took it though the perspex of his cage base earlier today. It shows the colours & markings well, but has a reflection of our skylight on back of Alba's head!! I will try and get a better shot tomorrow (night in the UK now so budgies sleeping under their cage covers.)