Using the search feature of this forum will lead you to dozens of posted pictures of these finishes....yet, no two will look much alike. (There are posted Tahoe pool photos that, if you did not know from the post, look quite like the Tropics blue). This is because there are so many variables affecting pictures of pool waters. Depth, time of day, building and wall reflections, adjacent color schemes, camera angle, quality of the camera, and sky conditions makes for great diversity in how these two finishes look in these photos. Bottom line is that choosing a finish from a picture has some significant shortcomings.
If I were in your shoes, which I assume is one of not being able to get your PB to refer you to his past pool customers who have one or both of these finishes, I would either go with the tropics blue w/out the upgrade; or better yet, pay for the upgrade so as to lessen the chances of having regrets with the finish that is installed. The Tahoe does have a slight blue green tint to it, which I believe you wish to avoid (that some, including me, do not find unattractive at all - this notwithstanding that I went with a modified tropics blue).
Consider the approx 15% upgrade cost as insurance against anguish and regret (as in feelings of regret every time you go outside and look at your pool...yikes).