1.) i don't like a color scheme that is 90% white (Drift is an awesome toy, but has a lot of white) but i like a vibrant mix. Contrast is a good thing for me.
Warbot Defender, or even the G1 Springer has a great look. it's easy on the eyes and even in less than stellar lighting, the colors pop. I like Springer's colors a lot more than his alt modes.

2.) there is room for Cybertronian modes. Like the WfC doesn't send mixed signals about where these guys live and hide. Personally, i like a few cybetronian mode characters over those TFTM '07 Poopformers that came out. those were just gray blobs with robot modes.
Hasbro can afford to have maybe ONE character released only in cybertronian mode (Fallen) but 2 or more in the movie line is pushing the fans a bit far.
defeats the RiD logic

 

I'm partial to purple and green color schemes. They display really well on my shelves and just kind of draw your attention in. However, I prefere the color scheme of my figures to actually match the character. Optimus should include red, blue, and white or silver. Hot Rod/Rodimus should be maroon with orange and gold. You get the point.

I've come to realize that I'm actually a fan of a more powerful alt mode. I love the movie version of Ironhide. That Topkick is badass! All of the Primes (including Beast Wars era) are pretty cool as well. Especially Cybertron Prime. Seriously, that is probably the best Prime we've ever had! I also have to give props to movie Starscream's design. I know he kind of looks like a big Dorito in bot mode, but the extra bulk up top makes him look more menacing to me.

 

I have a theory:

Earth Alt mode: main purpose is DISGUISE

while

Cybertronian Alt mode: main purpose is ENHANCE (firepower, speed, manuverability, etc)

since I mean, when you are fighting at Cybertron, disguise might not work very well. Its a full blown war, I mean.

 

I hate to be very general, but I really feel I have to here. For me, my answer for both is quite simply I want to see artwork done well.

There are definitely certain color schemes that work well. Certain color complement each other well, and a monochromatic color scheme can work, too. The key is that it simply has to be done well. Everything has a nice flow to it, the colors are applied and designed keenly, and all things considered will make a nice figure.

Alt modes are the same for me. I absolutely love realistic vehicles, but I really dig many of the "Cybertronian" designs as well. I do have to say that I have a tendency to drift towards Earthen modes more though.

I think I'd also add that too much of something can ruin things, too. Oddly, Transformers are something that I'll rarely prefer a "weathering" type of treatment too. I think that's something that looks well when done very sparingly.

The key for me is variety.  

 

Red trucks or cars.

 

I like black and orange. I think I prefer nice contrast so too much quiet colour is boring for me. Having said that, colour scheme isn't very high on my list of priorities when I choose which TF to buy.

As for the alt mode, as long as I can tell what it is, I'm cool. But often those with "can't tell what it is" alt mode have kickass robot mode (probably because they sacrificed one mode completely?) so I buy them anyway  

 

No, I didn't mean War For Cybertron Optimus Prime's vehicle mode.

I meant Cybertron Leader-class Optimus Prime's vehicle mode.

 

ah, I see. Sorry ><

Actually when I first saw the Cybertron Leader class OP, I drooled. I really like that mode. Cept it wasn't as shiny in the real robot.

 

Yeah. Luckily for me I had silver spray paint and other paints. But even without that, he's awesome. Fire truck with dual-function water/laser cannons for maximum butt-kicking and damage control action. Flying fire truck for sheer crazy awesomeness. And OPTIMUS PRIME, SUPER MODE! for making it suck to be a villain.

 

I like deco alot. I tend to buy repaints if they're a good deco of a great toy and is usually a brand new charecter insted of being a upgrade deco.

Optimus Prime ->Nemesis Prime = Will or might buy but Optimus Prime -> Nightwatch Optimus Prime = Not as interested.



I don't really car for vehicles modes usually except for Alternators.

 

1. Transformation color preferences?

Ahh, lesse... I personally like Hasbro's red and black separately or together. I don't know why, but I just love the red of their figures. (Example: Universe Inferno, Bluestreak and RoTF Swerve) Comparing Hasbro to Henkei is usually a little brighter as far as the red goes. ...Not that it matters, but in my case it makes a difference. ^^;

Purple is another color that I think works well. Henkei Astrotrain's gunmetal and purple combo comes to mind as does RoTF Skywarp's.

2. Alt Mode preferences?

I do particularly enjoy seeing Cybertronians transform into random earthen objects (toasters, vacuums etc) for one. Plane/Jet-formers also are something I'd like to see more of especially if they're don realistically (i.e. based of real world planes).
I'm not really picky though. I love when something unique ends up on the shelf. That said, I'm enjoying the sci-fi -eque/futuristic modes that come out. All car modes are fun to see translated into Transformers.

 

Despite my earlier post, I'll say that just about anything looks cool as a Decepticon in black sporting purple(ish) accents.