I'm looking to do something like this:
The areas that are "sunlit" are bright but still maintain the texture and line of the darker layers. How was this done? Is it some sort of blend mode? I have tried everything. If you could help me out, I would really appreciate it. Thank you so much.
I'll show you a quick example by adding some extra lit areas around the window...
First, on a new layer, I block in some color in the areas I want lit. I used a solid shape for the lower area and radial gradients around the actual window:
I then set the layer blending mode to "Soft Light":
There is no hard-and-fast rule here. You can get similar results with the "Overlay" blending mode, and it's worth playing with opacity levels as well as blending modes.
In reality, with an illustration like this, you would most likely hand paint a lot of the areas rather than only using solid shapes like I did and use a larger palette of colors.
Quick Tip: Painting With Layer Blend Modes in Adobe Photoshop: A nice quick article about painting with blending modes (highlights/shadows etc.) in Photoshop
Photoshop Blend Modes Explained: A good general explanation of blending modes in Photoshop.