I've always loved red and black. They go together well and it's probably my favourite colour combination (how stereotypically emo of me).
But recently I've started to develop a love of purple, pastel shades of purple too.
The only colours I struggle to work with are pinks, greens (because they can be so awkward to match) and cream, god damn that cream, it's all too frilly for my tastes. emotion_donotwant
Brown can be hard sometimes too.
Though I've never seen anyone make an orange avatar...do we even have any decent orange items that match? I've never looked. XD
I'm not very good at making avatars with orange or purple. I have nothing against the colors, I just can't use them to save my life. When I use green, its mostly as an accent color rather than the main color of my avatar.
I cannot make an avi using brown at all. They just come out some terrible thing ;_;
I try my best to work with every other color besides that. I've gotten better at making green avis that don't look like shrubbery...but only a couple hehe
Usually I avoid buying pastel items as I prefer more vivid colors, but it's not some set rule, there are always items I've found to be exceptions. (Usually I pick up froufrou pastel reis if i can get for <300k just because it is on the whole more poses and versatile for a good price compared to a 4 pose rig item that costs more)
I am a crazy person for blue, teal and all variants though. Seriously, I can't get enough blue into my invo, always want more.