The myth of the bright blue spark means nothing really. It could be all the colours of the rainbow.
A spark plug sparking out of the cylinder will be different as to under compression in the cylinder.
As long as todays coils "spark", (using a spark tester) that is all you need.
Now some manufacturers give you coil readings (like Honda) so you can test the windings.
Also coils can give different readings when hot and cold.