Hi! I collect Tanzanites. Yes, they do range in color, but the more the saturation of color, the more valuable the stone (in other words, less purple or voilet, and more blue). Most people prefer a stone in the Medium to dark range because they are known to give off pink flashes. That said, your stone looks really nice, and it looks like medium to me from the pics.
A concern should definitly be the setting of the stone, since it is not a hard stone on the Moh's scale. I find that one of the best settings for a Tanzanite, is a diamond HALO setting. With this setting, the tanzanite is set low into the prongs and protected all the around the stone in case you knock it. Lastly, make sure you have a Jeweler who knows how to set a Tanzanite, and confirms they have set them before. They can break if one doesn't know what they are doing. I had one Jeweler who wouldn't even touch one because he was too afraid to set it.