Hot strong colours bring something closer to the front, and cool grey colours send things to the back. Contrast and detail in the foreground always need to be greater, and recede into the background.
Even in a photograph you can see that the horizon is paler, bluer, and less distinct than the rosy red apple with a strong shiny highlight in the foreground.
Maybe look for a colour scheme first, then even sample colours from that image, and use them in your map. It doesn't have to be the same colour as the actual place. You could do it all in shades of blue, lavender and orange, or whatever takes your fancy - as long as the colours read right. In other words if you choose an image to sample colours from that happens to be a landscape, use the foreground colours in the foreground of your map, and the background colours in the background of your map.
I have an appointment in half an hour, or I would draw you a simple landscape to show you what I meant....
EDIT: apart from the hard line along the ridge of mountains in the background (which partly destroys the sense of depth in this painting in my humble opinion), this image by Johnathan Harris illustrates most of those points - cool pale colours in the distance, hot contrasting colours in the foreground. More detail and contrast in the foreground.
https://fineartamerica.com/featured/...an-harris.html
These paintings by Kristan Baggaley all demonstrate the same, and might provide a little inspiration for the colour scheme
http://www.derwentgallery.com/kristanbaggaley.htm