How the color is perceived is affected by the background, which is white in one case and an orange in other. There also isn't just a single color; it's a gradient. And the shape of the expansion symbol can affect how the gradient is perceived: the distribution of the positive and negative space will affect what parts of the gradient are more prominent. In this case, the vertical lines on the masterpiece version get more of the yellow that's missing from the non-masterpiece version. So if the possibilities are either that it's just the mythic rare color but it looks different for the factors I just listed, or that they chose to give the masterpieces their own color, but one which is nearly indistinguishable from the mythic rare color, I'm quite confident the former is correct.

I like how the old Premium Deck lands have a symbol that kinda pops from the background.

It is probably more of "Why should they have a different symbol?". I am not a printer, but I would imagine the black ink is probably the cheapest. They already know how that is going to look with their symbol and cards they print for each set as its factored in with commons. So what would be the added gain that would push them to add cost and time into their card art designs and printing processes?

I also don't see the ink cost as being a good argument. As a proportion of the cost to make the cards, the expansion symbol is completely insignificant. I don't think that sort of thing factors into their reasoning at all. That is, if they wanted to give it a different color symbol, they would do so, even if there were a tiny fraction of a penny difference in cost. The reason the basic lands have the common symbol is that they want them to have that symbol, not because they're cutting corners.

(Besides, if that cost really were an issue, white would be cheaper than any color.)