With a tropical dial the value is in the eye of the beholder.
Often these dials are only attractive when cheap. Once they cross into the hands of dealers, and the full pound of flesh is extracted, they loose a lot of desirability.
I love this because the dial cost $5 :
Now that said, once a watch has changed colour, leaving a solid high quality dial, that is valuable. Here is possibly the most valuable brown dial I know of:
Anyone can call a dial tropical, in fact often a watch might be described as tropical, swiftly followed by qualifying statements. (Degraded, damaged, dirty or clean, perhaps even, galaxy or dark chocolate). This variation in colours make a huge difference in value.
Here is a dirty tropical:
Tropical is just a group, and like any group the individuals in it vary wildly in desirability and value.
It is this judgement i find so appealing, and the hunt to find one without premium.