Sentence:  Almost all the specimens [of stamps] with this watermark are perforated. They are—the <WSD>amaranth</WSD> penny with two florets and two letters; the same with four letters, whatever the value of the minute figure at the sides; and the current penny with four letters, deep <WSD>amaranth</WSD> colour. 
Meaning of the word marked with <WSD> tags:  The characteristic purplish-red colour of the flowers or leaves of these plants.