A key is valid for the version of Moneydance you purchased, plus the next version. As you just downloaded Moneydance’s it’s probably 2019. To check if you key is valid for 2019 enter it in the Upgrading? box at https://infinitekind.com/purchase
If the current theme in 2019 is very bright with poor definition try FILE - PREFERENCES and use the dropdown next to THEME to try other themes. You have to restart Moneydance before a new theme takes full effect.