user6512: I want to select a colour which the computer picks up on and then only allows that colour to be viewed on the video, hence turning the rest B&W.
(for example like Sin City) 
What is the best software to do color pass effect for a film?

user6273: Mostly any commercial video editing software should be able to do this. Premiere Pro would be my go-to option, there are different ways to accomplish a color pass effect with it. You can set the color you want to be passed, the tolerance, chose if you want softened edges ... Premiere basically can do everything you can wish for regarding color pass. But then again, you should be able to do this with most prosumer-level editing programs.

user3592: Davinci Resolve Lite (link at bottom of page) is a free, fully functional version of professional colorist software.  It runs on both Mac and PC.  The most notable restriction to the lite version is that it's limited to 1080p output, which should be fine for most folks looking to upload videos to youtube, or show them on a standard HD TV.  Because Resolve is purpose-built for color correction, it provides a toolset that standard video editing software can't match.

6512: <p>I want to select a colour which the computer picks up on and then only allows that colour to be viewed on the video, hence turning the rest B&amp;W.
(for example like Sin City) </p>

<p>What is the best software to do color pass effect for a film?</p>
 6273: <p>Mostly any commercial video editing software should be able to do this. Premiere Pro would be my go-to option, there are different ways to accomplish a color pass effect with it. You can set the color you want to be passed, the tolerance, chose if you want softened edges ... Premiere basically can do everything you can wish for regarding color pass. But then again, you should be able to do this with most prosumer-level editing programs.</p>
 3592: <p><a href="https://www.blackmagicdesign.com/products/davinciresolve" rel="nofollow">Davinci Resolve Lite</a> (link at bottom of page) is a free, fully functional version of professional colorist software.  It runs on both Mac and PC.  The most notable restriction to the lite version is that it's limited to 1080p output, which should be fine for most folks looking to upload videos to youtube, or show them on a standard HD TV.  Because Resolve is purpose-built for color correction, it provides a toolset that standard video editing software can't match.</p>
