Is it that way in the record? APA 6th I think is set up to not change the title in the bibliography templates. If you change the output style setting to “sentence” it does change the word following a colon, to a cap. If you change the setting, make sure you save to a new name, and then change the output style in the manuscript you are working on, to use the new style (you may have to view all styles to see the new one in the list).
The image below shows where this setting is in the output style template.