I don't claim to know what exactly your trouble is when it comes to color landscapes nor an expert on the matter, but I gotta ask; have you tried hue-shifting?

Looking through even your best works, you tend to stick with straight color gradients (Light purple to dark purple, etc), because that's what you know best (Being a cartoonist). However, landscapes are a whole different animal because in real life, nothing is just a straight gradient, multiple hues blend together to make a cohesive whole.

My suggestion is to study up color theory again, minimize your use of shades, and look into hue shifting, which is turning one color into another through shading (Purple shifting into Red, shifting into Grey, etc).

The best examples of it are not just in other landscape pictures, but in pixel art as well since hue-shifting is an absolute necessity due to an inherent limit of color in the style.

http://www.pixeljoint.com/pixelart/33722.htm here's a pixel art example

and here's a digital painted example http://www.furaffinity.net/view/11314791/

They use relatively similar pallettes, three-four different hues of color at most, yet they all blend seemlessly. If that's what you want to do with your work, then that's definitely what you want to look into.

Well I do know basic color theory. Complimentary colors, some understanding of hue, value and chroma. So I know that smooth gradients don't happen in real life.

But over the years, my eyes have been improperly trained to see saturated colors, so I naturally use those, when I shouldn't. Usually when I use colored light sources, I tend to stick to the "warm lights, cool shades" rule. But I know there's m ore to it than that.

Not defending my technique, just saying why I think I'm doing it wrong. I'd LIKE to do better, but it's not so easy to learn new stuff when you're past your 20s.

I know how that is. I want to be able to play the piano so bad, but I can't because of the way I learned in Junior High music class. Everyone had a partner but me, so I had to play both parts by myself. And we learned one step at a time, naturally, so I learned to play the same melody with both hands simultaneously. Which sounds kinda cool since I can play the same thing backwards and forwards at the same time, but it sucks when I want to play normally. I try to play a chord in the middle of a melody, and my right hand stops and tries to play the same chord. I try to play a chord then the melody, and my left hand tries to play the melody at the same time.

In short, sometimes muscle memory sucks. :/

We've all got bad habits we need to break brudda, some have an easier time than others especially as you get older, true enough.

The way I see it though is any habit can be broken with persistance and patience. I mean, where were you with your art 10 years ago? Certainly not where you are now, that much is obvious. How many habits did you have to break to be at the level you are now. Numerous I'm sure. I say all this to make the point that you sir will meet your intended goal.

When? I dunno
How? Beats me.

But you will succeed, why? Because you've succeeded before. If you didn't, you would still be where you were ten years ago. That is, if you don't let age and weariness hold you back. *Shrugs*

That's all I have to say about that, good luck with your training.

What?
Everyone has to start somewhere.
Practice, practice, practice.

If you think you do better b&w then you should try coloring like  shin0r0z

He does all or most of his shading in monochrome then puts a layer of color over it and uses a layer blending mode to combine them.

Reminds me of Mount St Helens with the lake like that.

looks incredible!

Its fairly safe to say that if your values do not work well then no method of adding color is going to fix it.
In this case I think it is fairly safe to say that the problem is that your value separation is not strong enough. Youre foreground objects are using very similiar values as everything in the background. Rimlighting them is probably doing more harm than good at this stage.

That makes me jealous of your skills.

Not bad~

Looks great

You realize this is the perspective of looking up toward a woman's crotch from about her foot level, don't you? Hence, the Freudian title.