18 colour logos to grey scale

Design details: I have 18 business logo's (facebook, tripadvisor, yell etc.) that need to be changed into a grayed out version with transparent background for use on a website.

A good example of what i want can be found at the bottom of this page https://uk.fiverr.com/categories
Ideas for the visual style: Grey!
Where the design will be used: business website
Extra notes: I have attached some examples of the logos i need changing.