Sure, now I understand which themes you are talking about, not about the project theme.
Thanks for reporting this, don't think much can be done about it. That interaction is one of the oldest widgets, existed before the power of Themes appeared for projects. Just want to give you a tip: for those interactions where it is available, check the option 'Theme colors' under Custom so that the learning interaction fits in better with the Theme colors palette used in your Project Theme. Here are some links about theme colors and themes:
Theme Colors - Captivate blog
Exploring THEMES (and templates) in Captivate | eLearning