Hi Harry,
I think I know what's happening now... And I think it's a bug.
0) I have an external SD card (/sdcard1), and have an internal SD card (/sdcard0).
1) When I installed OsmAnd~, the default location is /sdcard0. So, /sdcard0/omsand/voice/en-tts/_ttsconfig.p was created.
2) I set the data folder to be /sdcard1, and then downloaded the map. The program cannot locate /sdcard1/omsand/voice/en-tts/_ttsconfig.p because the file was never created; therefore, I redownloaded the latest voice pack on /sdcard1
3) However, the program scans the folder of /sdcard0, and prompts me to update the tts package. I updated, but that does not change the files in /sdcard0. So it keeps showing blue and can never turn green.
Essentially I think that's what happened... It's a really trivial thing. Thought it's fun to find out why, and good to report a bug!