How many months does it take for stretch marks to fade to skin color?

Depends but several: Stretch marks are defects in the collagen cross links in the skin. The risk to get them tends to be inherited--blame your mother! seriously though, it will typically take from 5 months to a year or more for a significant fade to silver or white to occur. It is a gradual process generally.

6-18: Depending on depth and width redness will gradually fade in abut 6 months to over a year.