Conscience speaks softly, yet it may have the loudest resonance. When we are water baptized, it is cleansed so that we have unblemished/clear conscience.

1Pet3:21
and this water symbolizes baptism that now saves you also–not the removal of dirt from the body but the pledge of a good conscience toward God.

The book of first Corinthians discuss plenty of it. And it is indeed shed a light in the gray area that may not have been explicitly mentioned in the bible.

David, the man who after God’s heart, is a conscious-stricken man that he, in his power, wouldn’t allow harm to Saul even it is clear that Saul has attempted to kill him. Not only once that David has the opportunity to kill Saul but twice.  And both times, he stayed true to his conscience.