Here is a link to some rather fin tanzanite in large sizes. the best color is a very deep, pure blue with an overtone of violet and the prices on this website for their best stones are about $700/ct:
Lighter tones and muddy colors with brown or grey tints are less valuable. It is hard to tell from your photos…I’m thinking I see some grey in the top picture, maybe a little in the bottom one, but not sure. What I do see is large windows in both stones which wash out the color under the table in both of them. So both of them are cut a pavilion angles which are too shallow and, if I’m right, the face up color will improve quite a bit if the stones are recut. The color you see under the crown facets at the edge is basically the color you should be seein under the table, too, in a well cut stone. I would caution that all stones below about 2.0 in refractive index will window when tilted enough off axis, but your tanzanites are RI=1.69, and, at the angle of your photo, I don’t think they should be windowing as much as they are. To determine whether they are windowing due to incorrect angles, you need to look directly down into them at right angles to the table. Put your finger under the stone (held in your other hand) and wiggle it. If you can see the finger moving under the table, you have a window due to incorrect pavilion angles.
IDK what you are paying for these, so if I were you I would look at the link I sent and at a few other tanzanite sites and try to match color with your stones and see whether you think you are getting a good deal. Short of involving an appraiser who does not sell stones and doesn’t offer you any, a real indepedent appraiser, this is the best you can do. It does take a while to develop an eye for color, but if what you have is vastly different in color from comparably priced stones on the internet, you will know you are not getting a great deal.
As I said, the color I can’t be sure to judge accurately from your pictures, but the windowing I am pretty sure about and it does indicate to me that these are not of the best quality, or they would have been cut to show their color to best advantage. If you decide to buy these, they can probably be recut to proper angles without a loss of more than 15% or weight, for about $200.
Hope this helps. It really is risky to be buying gemstones without a lot of experience in the business or an expert consultant who has not conflict of interest.