docs: changing letter or letters to substring

subjects/ascii-art/color/README.md

@@ -4,16 +4,16 @@
 
 You must follow the same [instructions](../README.md) as in the first subject but this time with colors.
 
-The output should manipulate colors using the **flag** `--color=<color> <letters to be colored>`, in which `--color` is the flag and `<color>` is the color desired by the user and `<letters to be colored>` is the letter or word that you can chose to be colored. These colors can be achieved using different notations (color code systems, like `RGB`, `hsl`, `ANSI`...), it is up to you to choose which one you want to use.
+The output should manipulate colors using the **flag** `--color=<color> <substring to be colored>`, in which `--color` is the flag and `<color>` is the color desired by the user and `<substring to be colored>` is the substring that you can chose to be colored. These colors can be achieved using different notations (color code systems, like `RGB`, `hsl`, `ANSI`...), it is up to you to choose which one you want to use.
 
-- You should be able to choose between coloring a single letter or a word.
-- If the letter is not specified, the whole `string` should be colored.
+- The substring to be colored can be a single letter or more
+- If the substring is not specified, the whole `string` should be colored.
 - The flag must have exactly the same format as above, any other formats must return the following usage message:
 
 ```console
 Usage: go run . [OPTION] [STRING]
 
-EX: go run . --color=<color> <letters to be colored> "something"
+EX: go run . --color=<color> <substring to be colored> "something"
 ```
 
 If there are other `ascii-art` optional projects implemented, the program should accept other correctly formatted `[OPTION]` and/or `[BANNER]`.