Separate elements with Pins
Avoid making all of your changes on a single adjustment brush layer. Instead, Choose the “New” option in the adjustment brush panel to lay down new pins when working with separate colors or touching up new segments of an image. You can then go back and make changes to exposure, and contrast to the entirety of a specified pinned area.
Pay close attention to edges
When colorizing an image, take extra care to make sure that your colors aren’t bleeding over hard edges. Likewise, use a feathered brush for subtle transitions between similar colors. Zoom in to your image to examine the fines details of your shot.
Should you make a mistake, don’t fret. It’s easy enough to convert your brush into an eraser. In this particular scenario, you may want to consider temporarily turning on Lightroom’s Auto Mask option to make the clean up process a bit less excruciating.