Those "flaps" are your labia minora. It is very normal for one to be longer than the other. Purple is a very normal color. All labia minora look very different, and they range in size, texture, and color.
No, that is not a disease. What you are explaining is normal and common.
The answer is learning to love what you have and realizing it is not only normal but common. This is not a problem. It is normal. Look at tumblr's 'Large Labia Project' to see some of the variation that exists in labia - don't worry if you don't see a similar one, like I said, no two labia are the same. In survey's, men either like a long labia, or don't care.
Porn has RUINED what women think their labia should look like. Pornstars get their labia cut off and bleached. It is NOT an accurate depiction. If you look at porn from 10-15 years ago, they all had normal labia, ranging is size, color, and texture. In fact, the majority had labia that was 2+ inches.
No, that's absolutely normal. I'm assuming you're talking about your inner labia (labia minora), and each woman is different when it comes to what her labia are like, especially her inner labia. Some women have labia that are longer and show out from the labia majora, some women have labia that are asymmetrical in length and differ in color, and some women have very small labia, which is what society and men have decided to be "normal" and I laugh at that. A lot of women, particularly those in porn, undergo surgery to get the "perfect" labia and basically genital area, it's ridiculous.
I'm like you, I have asymmetrical labia, one is pretty significantly longer than the other and a bit darker/more purple. It used to make me so self conscious and then at some point I stopped caring. I realized each woman is different "down there" and I was just fine how I was.