A Word Puzzle

Find a series of words using the following clues:

1. The first word means "an outer garment".
2. The second word refers to something that tells time. This word is formed by replacing a letter in the first word with another letter.
3. The third word means "to impede or prevent". This word is formed by replacing a letter in the second word with another letter.
4. The fourth word is the name of a dark color. This word is formed by replacing a letter in the third word with another letter.

Find these four words.