Hello,
I want to share a program I originally made for myself because I couldn't find anything similar. I thought that other people might like it, too, and if so then that's great.
My program is called the 'NDS Palette Randomizer' and does exactly what the name implies; it can randomize all Pokemon color palettes in all NDS Pokemon games (Diamond, Pearl, Platinum, HeartGold, SoulSilver, Black, White, Black 2, White 2).
I have build in different randomization modes sorted by most to least random:

• Completely Random - randomizes every hue of the palette seperately and assigns it a new brightness and saturation value as well.

• Randomize Hue - Leaves saturation and brightness as it is and just shifts the hue. It is possible to get a Pokemon with almost the original set of colors or something very different.

• Slightly Vary Original Colors - Shifts the hue, saturation, brightness of the palette slightly to create a subtle change. Here and there a more changed look is thrown in.

• Color by Type - Assigns a predetermined type color to the Pokemon to make types easier to identify. Useful for beginners or when types are changed with the Universal Pokemon Randomizer.

• Color by Evolution Family - The whole evolution family will use a single palette and therefor look similar.

• Color bias - You can increase the likeliness of a specific color to appear. If you choose yellow you will get more yellow Pokemon.

• Change one Color - The Pokemon stays the same exept for one randomly chosen color. You can end up with a Charizard with violet wings, a Pikachu with blue cheeks and a Bulbasaur with a red bulb.

I have included a manual in the actual program itself. Click on the 'help' button in order to view instructions.
I hope that you will enjoy my work as much as I do.
Download
You can download the newest version HERE.
It should be compatible with all languages and NDS game versions. If you are experiencing problems, please notify me.
This version includes a beta version of the trainer color editor. Works for Black/White (2) only.
Click on the edit trainer button, click on the hat/skin/.. buttons, choose a color, close the trainer window and your chosen colors are applied to your trainer avatar.
Currently working on..
.. an editor to modify the colors of your trainer avatar.
The colors are applied to the overworld and in-battle sprite. All you have to do is choose a few colors.
It already works for Black and White, currently working on B/W2.