I wanted to share with you a QVW I've been using for a while now. First off, I'd like to mention that it is by no means my idea/concept, I've merely adapted (striped-down) Adam Booth's fine work from 2013 to fit my own needs. If you're looking for a more in-depth version of this application, I suggest you check out his original application,QlikView Colour Tool V1.qvw.
This application asks you to select a colour using the RGB input boxes which you can adjust using the sliders to display your selection, along with 4 similar colours (2 lighter and 2 darker). These colours are not just a few shades lighter but have subtle differences that help me when I'm building applications...especially the ones that contain Heat Maps!
I've also included the 2 main tips I use when naming my colour variables that makes my life a little easier, especially if a client decides to change their corporate colour scheme years after an application has been built!
Update: Including closest ARGB value of Primary Colour (thanks to John Witherspoon)
Update Update: Changed script to John Witherspoon's idea. Bother versions of the tool now exist in the script so feel free to use which ever one you prefer (hint - John's is better!)