WIP-Heldarken(World for DnD)

[Chashio]

... and a deper color in the open seas to give a look like it increases in depth.

One way to do this is with a layer mask technique. Here's a tutorial for how to set up and manipulate layer masks in GIMP: GIMP - Layer Masks If you scroll down a ways you'll see a picture with a face being covered in blue by stages. That's the general idea of where this goes... but not quite how we'll get there.
Fill a new layer with your water color and give it a white layer mask. Because it's full opacity, turn the layer opacity down in the layer panel so you can see through it and know where your land is. Now... Instead of using the rectangular select tool and the fill bucket with shades of grey, use the freehand select tool (the lasso) and a large round brush colored black with opacity set between 10-50% (if you want more levels of depth changes, use less opacity, if fewer, use more). To begin, select the shallow water including your land masses (make sure the tool mode is set to add to selection, and if you want softer edges, turn on feather edges); use your brush to make one pass over all of your selection. Use the select tool to to grab the next level of depth (adding to what you previously selected) and make another pass with your brush tool. Repeat this as many times as you want. Finally, deselect everything and use the fuzzy select tool (have to be on your map layer) to grab your landmasses, and (on the water layer mask) fill that selection with 100% black. Note: the lake in my example was not selected in this stage, so it got to stay wet. Deselect everything and set the layer mode to whatever you want (mine is set to Multiply).

Screenshot Animation


Example of Feathered Edges