How to randomly change color of single characters in a string of text

I have a string of text n-characters-long (colored say in black) in a div and I would like to obtain an animation where:

• a n quantity of those characters (how many characters are affected is a parameter that I would like to set) changes color from black to say red
• in any given interval n randomly-chosen characters within my div should change their color (start and end color is another parameter I would like to set)
• I would also like to control the duration of the animation (for example, for how long the new color is kept before falling back to the initial one)

With javascript this should be possible I guess, unfortunately I don't know Js enough to write the code. Is there any snippet that already does this animation? Any good advice or help?

Thanks! P.