Here's a quick comparison of my different dark blue tones!
'Navy Blue' is one of my most popular colours for cake decorations - I would suggest going for either my Navy Blue (Very Dark) or Navy Blue (Dark) tone.
Navy Blue (Dark) is a good, strong blue - perhaps some might call it a 'French Navy' - it's just not quite as intense as the Very Dark tone which is also a popular choice for my customers.
It really depends on the overall colour/design mix of the cake you have in mind!