脸色苍白

have a pallid complexion

脸色红润

have a rosy complexion

脸色惨白

have a dead white complexion

病得脸色发黄

have a yellowish complexion due to illness

脸色不好

not look healthy

他的脸色比过去好多了。

He looks a lot better than he did before.

一看脸色就知道

know with a glance at someone's expression

干吗要看别人的脸色行事？

Why should one do things with one eye on other people's expression?