Here's a plugin that lets you convert your layer/output video colours to R,G,B levels with cursor control and adjustable sample size in the preview. You can then hook up your colour information to synths, etc.
You'd be running blind if you used it with b7, so b8 is the go.
Place plugin in user/library/application support/vdmx/plugins and add it as a plugin once you're in VDMX. You will want to add a preview for the plug if you don't have it already. Assign X and Y pos individually, and you may need to reverse these(iex=y), to the preview x and y. Assign "button" to the preview mouse down. Choose your input image. I assign a controller to the sample size and buggerize with the posterise levels until I get some dynamic colour information.Now if you click and hold in the preview you will sample colours and see the sample box moving with your cursor ,if not boost its size. The outputs appear as data sources which you can then assign to control surface faders or sliders and put midi senders on there (b8).
Be careful with the sample size especially if you have busy or dark visuals.
If anyone has any suggestions please let me know because I know it can get better. Have fun.