怎么知道自己的英语进步了？

以前写的英语句子：

It's a blue car.

It's a green car.

现在可以写：

It's a teal car.                              teal: a greenish-blue color

以前写的英语句子：

It's a yellow sweater.

It's a brown sweater.

现在可以写：

It's an amber sweater.            amber:  a yellowish brown color

以前写的英语句子：

It's a write envelope.

It's a  black envelope.

现在可以写：

It's a buff envelope.                    buff: a pale yellow-brown color