First thing: it depends on how the screen we are looking at is adjusted. The first thing I do with a new computer/graphics card/monitor is to adjust the colours. Because of that, a designer that made some graphics for a site I was making was surprised to see that on my monitor the colour he chose was purple and not blue, as he saw on his computer.
Second: simultaneous contrast does that to our vision. We are always trying to compensate the colours we see, that's why light grey close to yellow looks blue and vice versa.
To me, it looks light blue, but I can also see that the photo does not have a good quality, as it was taken with a strong light behind the dress and probably adjusted to make it visible, as it was most likely too dark.
Cheating and looking at the pixel values I can see it has more blue that green or red.
This is the average colour: #7E88B8
PS: not all people see colours in the same way, so talking about colours it's never a straight answer.