Unless you want to be the stereotypical scrawny (or overweight), unhealthy vegan, the vegan junk food diet is not for you. This basically means you eat a bunch of highly processed foods, potato chips, soda, candy, etc. If it has color, you avoid it.
Food with color is where most of your nutrients come from so if everything you eat is a shade of white, you'll be missing key ingredients to a healthy plant based diet.
The nice thing about being vegan, however, is that you can eat white foods without feeling guilty, but eat lots of colorful foods, too.
A lot of vegans think diet doesn't matter, but they're not looking at the whole picture. If you're an unhealthy vegan, chances are good that you'll need to take more medications and require more healthcare down the road. Both of these generate byproducts that are harmful to the environment (air, land and water), which directly affects the lives of animals who live in the environment.
Medications are also tested on animals, so if your poor diet requires the use of more medications, that's not very vegan. It's impossible to be a perfect vegan and it's impossible to avoid all medical needs, but we should all do our best to minimize our impact on the environment and reduce our need for medications tested on animals.