This is a bug in Android Studio.
This has been raised as an issue:
(“Android Studio suddenly close without any warning when try to change color in Vector Asset or Image Asset”), see issuetracker 138910326
You can add your experience to the issue.
You can change the color manually (in a text editor) until it is fixed.
see also issuetracker 140642034, 132316444, 67980679, 37061710