Which paint primer should I Use?

[shayna]

I am painting over a dark blue and a bright green color with something light. I'm thinking of doing a light airy blue or turquoise color. What I need to know is, what kind of primer I should use. I was told by a guy at Home Depot that I should use "a color-hiding" primer, because I'm painting a light color over a dark color and need to hide the old paint. So, what is that, or do I need that? If not, what should I use? Also, do I still need to put on two coats of paint after I use the primer, or can I just do one? And how many coats of the primer do I need? I'm going to be using a latex based paint. By the way, I was wondering about VOC's and whether or not those are a concern once the fumes have gone. Are those only in the fumes, or does the paint always omit that? Please only give me a straight answer, don't just tell me it's a matter of opinion or link me to a site that talks about primers because I need more details. Thanks for all the help. I want to get this done before school starts.