I need to make buttercream in these colors. What colors do I use for Navy blue and mustard yellow?

Per the chart, it says "NAVY BLUE Royal Blue and Black" and "WARM GOLD Use Golden Yellow with just a touch of brown".  Let me know if these colors are not true...

Americolor actually has a navy blue color if you can buy them in your area, I just bought it a few weeks ago but have not tried it yet.  I have also used the royal blue/black but ended up with more of a grey blue color.  Perhaps I used too much black, just add a very small amount.