Yup. Some people like the murdered out look, while others nerd out with color and replace everything possible down to the smallest bolts on your derailleur or shifter with something bright and colorful. At the shop I worked out a fellow co-worker literally replaced anything he could on an old Bianchi Martini XC frame with anodized purple. Not my thing, but not my bike either. Go nuts if you want to.
My wife's bike is going to be covered in blue; nipples on the wheels, shifter housing, headset, headset spacer, etc. Pics to come for sure during the shakedown ride this weekend.
Your imagination and wallet are the only things stopping you.
Good places to add color could be rims, hubs, headset, cranks, bottom bracket (if external), stems, bars, grips, seatpost clamps, yada yada yada... Colored nipples on otherwise plain looking wheels can also add a ton of contrasting color. Bottom line is there are literally colored components for anything you could possibly replace on your bike.
