Consider tweaking colors to draw eye to differences

Thanks so much for the kaocha, I am really enjoying using it!

Some of my integration tests include the comparison of largish data structures. It can take my eyeballs a while to find the diff between expected and actual in these data structures.

I do sometimes use the search feature in my terminal to search for + and - and that can help and I was thinking focusing only on the differences, as #13 suggests, would help.

But I am also thinking perhaps a different choice of colors might help. I like the choice of colors chosen for differences, but I find that the red can take a while to spot because it is already used in non-diff syntax highlighting.

My initial thoughts are:

1. change the red to something else in default syntax highlighting, maybe blue.
2. take advantage of background colors to really draw the eye to changes. We might even be able to keep the normal syntax highlighting foreground colors with this scheme.

I am happy to give some color schemes a whirl for review, then a PR with changes, if there is interest in this idea.

issue 中没有提到文件或测试的名称。定位应用语法高亮和 diff 颜色的代码，然后检查现有输出及任何相关测试；当达成一致的颜色处理方式能够让变更更容易被发现，同时不破坏正常的语法高亮时，即视为完成。