shall we colour it blue?改为祈使句！

我不决定 colour 能不能做动词，不过，根据你给的例句，应该是能做动词。。
那就改为：Colour it blue!
或者是：Paint（画） it blue!

Color it blue.

Color it blue,please.

Please color it blue.

let's colour it blue.

Let's colour it blue,shall we?
我印象中是这样～