Today marks 55 years since Eswatini adopted its current flag on 5 October 1968. Based on official flags, it seems like a bright blue is standard, despite depictions often featuring dark blue. - eviltoast

There does not seem to be an officially defined shade of blue, but a bright blue is seen in for example these pictures of prime ministers:

Many do believe that it should be dark blue though, as shown by a quick ducking. On Wikipedia, there seems to be an ongoing edit war about it.

Then there is the color of the feathers, that allegedly where changed from blue to grey in 2011, but sources are not 100% reliable.

Wikipedia article about the flag.