First tell us about your background such as age, sex, ethnic background and etc. That'll help narrow things down.
Anyway, I think I sorta know what you mean when it turns redder when you go outdoors. I notice that with myself too at times. However, I don't think it's really turning red but the fact that sunlight through thin skin is making the acne appear redder.
There are different causes of acne. One is commonly puberty when somthing about your hormone levels rising which makes your oil glands produce more oil and bacteria and oil together clogs up pores, then it swells and become a pimple. The other cause in my case is hereditary. I'm sure there are other causes that i'm unaware of that you can look up on.
I went to see a doctor about my skin a month ago and he put me on tetracycline pills and a topical benzyl peroxide topical agent. I don't use the benzyl peroxide much because like neutrogena face wash and etc, repeated use drys up my skin way too much and peels. Anyhow, I have noticed that I haven't been breaking out as much lately which is good. If all else fails, then I guess i'll have to try a powerful solution called accutane. I've heard of its serious side effects and it's demanding price, but the testimonials are overwhelming. Anyway, hope that helped.