Ideally, inheritance lines would be grey, or settable to a different colour to the colour of association / composition lines. Same for any other subtype-supertype relationship. In the attached example, you can see how helpful this would be!
My ideal would be
a) line colours settable e.g. just 'all assocation type lines' and 'all generalisation types lines' - i.e. only 2 settings
b) grey would be the default for the second type of lines.