One thing I have learned from years and years of painting is that it is absolutely imperative to mix up colors and have a lot on hand if you plan on painting large, painting over the course of multiple sessions or may need to touch something up later. Nothing is harder than trying to match an exact color. And acrylic painters know that the dried color is not the same as the wet color. Acrylics tend to visually darken when dried.
So right now I have a tub of "old map paper," a tub of "old map faded ink," and "straight up pure white."
Just the map lines took like 3 sessions... small tight work like this with the fonts and numbers and lines can really make my hand achey.