Do you normally wear makeup? If not, don't wear it for picture day and then stop because people will think you look way different without it. Anyway, if it isn't to late where you are at, go get some foundation, powder, etc. Maybe get one of those "pimple sticks." (It looks like lipstick but it's not..you're mom might have some) Yes, a bright colored top is great for picture day!
As for the actual pimple...what I normally do if it's a white head is pop it. That's all... If it looks really bad or hurts alot after that, you can put alcohol on it. Yes, it will sting, but it dries it right up and gets everything out of it. Then again, I don't have acne...I just get a couple huge pimples every once in awhile. For my 9th grade pic day last week I had a scab from a pimple on my lip, but it looks better than the pimple in my opinion. If it isn't at a white head yet, put some minty toothpaste (mintier the better) tonight and it should bring all the ickiness inside the pimple to a tip by morning. As for future references...get Clarisal (spelling?) The little wipes without everything else works great if you don't have acne or pimples too bad. Don't worry about it though...you know those people that have really bad acne? Well no one makes fun of them, right? Everyone hates pimples...just try to think, no one probably cares. They're probably worried about themselves. But seriously...think about it. If you saw someone in the yearbook with a pimple on thier face....are you really going to care?
Hope I helped and good luck! ( :