The stamp was a dark, dull blue colour with a heavy black postmark.

这枚邮票是模糊的暗蓝色的，上面盖着一个粗黑色的邮戳。

《柯林斯英汉双解大词典》

The stamp was a dull blue colour.

邮票是晦暗的深蓝色。

youdao

A blue sheet had been hung behind Rosenberg, to deflect glare, and there was a dull hum in the background, perhaps from cars on a nearby street.

一块蓝色薄板挂在罗森博格身后用来偏转强光，背景里能听到隐约的嘈杂声，也许是附近街道上汽车的声音。

youdao

I saw it clearly -- all a dull blue, with a horrible veil over it that chilled my bones;

VOA: special.2009.05.16