сиёҳ

сиёҳ: black

Мӯи шимпанзе сиёҳу сахт мебошад.
The hair of a chimpanzee is black and hard.
Дар кишвари Дания лолаи сиёҳро парвариш мекунанд.
In Denmark they grow black tulips.

Bonus:
абри сиёҳ: black cloud, rain cloud
рӯзи сиёҳ: black day i.e. sad day, day of disaster
тахтаи сиёҳ: blackboard
сип-сиёҳ: very black
If you need to review colours you can do it at Memrise: Tajik Colours. (You need to log in, but it is free.)

сафед

сафед: white

Ранги сафед аз бисёр рангҳо иборат аст – зард, норинчӣ, сурх, сабз, кабуд ва гулобӣ.
White is composed of many colours – yellow, orange, red, green, blue and purple.
Роҳи сафед!
Safe journey! (Literally – white road)


Bonus: 
Do you know what тиллои сафед is? You can use google image search to find out.
There is a cool way to say “very white” in Tajik – сап-сафед. There are also cool ways to say “very blue”, “very red” etc.
If you need practice with colours you can learn them here: Memrise – Tajik Colours