Colors are subjective and I believe we do not all see them the same even if we've learned to label the same colors the same names... The real thing that matters is whether the fabrics work together for you.
Even from the same manufacturer, just like with yarn it is best to get all your yardage from the same bolt/dye lot. One of the reasons many of us like dealing with Kona solids is we feel they keep very true to their color standards and so you can reorder the same color even years apart if needed. However, colors between manufacturers even with the same names can vary quite a bit. Not only the dye formulation but in the processes used, and the griege goods (the raw woven cotton) have differences in thread weight and fiber length and all sorts of things that make fabric react to light.
I would say that while close, there is a point on the color wheel where a color is more yellow than green, or more green than yellow and that while similar, they are different. While I might call either of them separately as "yellow-green" together I would see the difference.
Indigo is a plant pigment, it is a specific color. Blue Jeans were originally indigo but have been artificial indigo as long as most of us have been around. I'd say that Navy is an enchanced and stabilized dark indigo. So in terms of fabric, I'd say that if it was woven with two colors of thread (white and indigo) the fabric would be "Denim" but if it was all over dyed it would most likely be cotton called Navy
