White is usually a dead pixel. Blue may be just a frozen one. There are things you can download to fix it. It is usually just a video that flashes your screen a shit load of different colors.
I went through about 5 PSP's when I bought mine from best buy for just that issue. Each one I bought seemed to have 4-5 dead pixels on the screen. I think it is 3+ will warrant you a new one. But usually you can return it within 14days or however long for them to replace it.
I sold my PSP before last summer, and I was wanting to get another, or a DS. Anyone have an opinion to which I should get? I'd like to play FF 1&2 + Tactics, along with all the movies on there. So I'm really turning to the new slim PSP. Anyone?