Copyright Infringement: Do social media companies (Twitter, et al.) pursue logo violations?

Well, you are not "coloring" a logo. At best, you are creating a colored silhouette of their logos that directly link to their sites. And any organization that claims that coloring their logo is copyright infringement is full of it. None of them would succeed in an infringement lawsuit for doing it the way shown in the figures. Period. Unless you and your lawyers don't show up to court, that is. But your lawyer(s) are concerned that they will sue. Well, the companies owning those social networks do have the ability to sue, regardless of their ability to win. Let me be blunt: there is no way to prevent anyone from suing you. Ever. That has nothing to do with their ability to prevail in court. And if your attorney can't come to grips with that, he/she probably isn't the best lawyer for you to have.

I don't know if these companies pursue logo violations. From one point of view I rather doubt that they do, because it would take a major amount of their time and energy. In simple terms, from a cost-benefit standpoint, it wouldn't make sense. Then there's the Fair Dealing-Fair Use argument under copyright. That could make taking any action difficult. But... Logos would usually fall under Trademark law. Trademark law is different. If you don't defend your mark, you can loose it. It would also depend on how much damage the logo violation would cause. If it was a small, virtually unknown site, who is going to see the modified logo? If it is a major site, where millions will see the modified logo, there's a far greater chance that they'd take action. Of course the smaller site would be more than likely to fold under a legal attack, while the larger site would have the money to fight. A lot is going to depend on why you are modifying the logo. If it is a negative article (Facebook is evil) and you modified the logo to include devils with pitchforks, you'd have a damned good argument that you were using the logo in a creative way, to criticize the company. Really, you need to talk to a lawyer about this, specifically one versed in Trademark and Copyright law.

"In other words, tell me how to get the corporate attorney's in my organization to stop worrying that Facebook, Twitter, YouTube, Pinterest are going to sue you for promoting their social network." You can't. It is the job of your corporate attorney to protect you. Companies need to defend their trademarks if they don't want them diluted. You never know what agreement was made with another company, or perhaps they don't know yet that their logo is not used correctly.  Your attorney only knows what agreement was made with your company and has to stick with it. Most companies do allow a black or white color of their logo on a color background.