I'd recommend to start with:
:help coloring
In particular, some conventional names are listed under
:help group-name
The command to change colors is :highlight, so if you just want to
customize some colors of your current color scheme, that should be
enough.
If you want to develop your own color scheme instead, I'd follow the
other suggestion to look at existing color schemes and start tweaking.
This reading may also be useful:
:edit $VIMRUNTIME/colors/Readme.txt
There is a plugin called Colortemplate (developed by myself), which aims
at making the task of building color schemes easier. But it doesn't hurt
to know how things work in Vim first.
Hope this help.
Life.