To change the colour scheme or colors in general in Putty is actually quite easy, open up putty and make sure that you have loaded the default settings.
Mark the point “Default settings” and hit load.
Once this is done, you are ready to hit the “Colours” tab to the left, once you get there you will have the options to input your own configuration, the page should look like this:
You can use my color scheme if you like, you can find the details here: Color scheme