It looks like an old tetraploid TB.
There are several light blue historic TB's that resemble this one.
While I didn't have a photo handy to compare with it, 'Claire de Lune' came to
mind immediately, and might be a possibility? It reminds me of 'Sierra
Blue', but I don't think that's right either?
I have a very similar one in my yard that came as a hand-me-down from
somebody, and I have hesitated to declare mine to be 'Claire de Lune' as the
veining on the claws and hafts is slightly different from that in the only
photo of 'Claire de Lune' that I've seen, puplished in 'ROOTS'. yours
seems to me that the veining might be less than on mine or the real 'Claire de