There are a number of old threads that reference this colour, but nothing regarding Tamiya that I could find.
Does anyone have a good way to mix ANA 610 Sky Blue with Tamiya acrylics?
From this post, XF-23 appears too green to use as a base:
X-14 looks like it may be 'too' blue?
I wondered if white with a drop of XF-50 Field Blue, or possible XF-18 Medium Blue?