Okay so I changed my image to 640X480 with a resolution of 300. My image is now only 2X3 or so, is this enough for the threadless people to work off? My version doesn't look real good, I must be doing something wrong. Is resolution different than dpi?

I am currently working on a design and I am having issues with minor color discrepancies. For some reason colors have shifted in tone while I was working on it. This is a huge problem because you can only have four unique colors, thusly it might prove as a denied submission. I am currently manually changing the colors, if anyone has any idea why this happened let me know. Don't tell me I am an idiot either, as that is not very helpful.