what wilton icing colors can I mix to achieve a nave blue?

Start with royal blue and add a little bit of black.
Here is a link to a thread that discusses this topic.

http://forum.cakecentral.com/heres-a-mixing-color-chart-ftopicp-5977371.html#5977371

Jibbies

i used blue and made it as dark as i could then slowly started adding a little black. I would color it day before because mine got really dark the next day.

I would have to suggest using the Royal Blue and make it a nice deep color....then add black, a little at a time to soften the Royal Blue. I personally have not done this, but it seems the most feasible if you only have the Wilton Colors available to you. There is Navy available by Cake Craft. It makes a nice deep navy, but even using this, I tend to start with a base of royal blue.

Hope this helps,
Gayle

I used violet and sky blue (I'm almost positive it was sky blue, not the royal - ?) mixed with a little black added and got a dark navy.

I use royal blue and purple to get a deep blue, and then gradually add black. Let it rest for a while because it will darken over time, especially if it is sitting under bright light.