More or less Theme Manager is the "Plus" version that allows for applying .suite files, making your own suites, and custom tuning what gets applied. MyColors pretty much just applies .mycolors themes. They become redundand if your an Object Desktop Subscriber (as the new Theme Manager isn't available as a standalone yet), but alot of people who buy MyColors themes are looking for a 1-click solution, which is what the MyColors app is for (there's no coincidence that the interface basically has one big "Apply" button).
