Snagit captures images appear much darker than they did before Snagit captures produce dark images. As you can see from this screenshot (not mage from snagit): http://prntscr.com/m3f8ap the colours appear darker and washed out.
You should probably tell us what version of SnagIt you are using as well as the version of your operating system. I have seen posts about this over the last six months or so and I could have sworn that TechSmith released an update that corrected the problem.
I guess the first thing I'd suggest is to ensure SnagIt is updated to the latest minor version. If you aren't on the latest version, perhaps download and install the latest, then apply any updates and see if the issue goes away.