Why do some windows files and folder names appear in blue and some in black

Entries in blue are NTFS compressed folders/files. Turning off system restore will delete all restore points which take up space. You can enable it again after turning it off. The disk cleanup advanced tab allows you to delete all but the last restore point which is probably the safer option.

You can adjust your trash and restore point settings to tell them to use less disk space. If you don't use hibernation, turn that setting off, then delete the hiberfil.sys file which is most likely the size of the amount of ram you have installed in your system.

Windirstat can also help you locate large files/folders that you may be able to delete.

http://windirstat.info/

You can reset your $TOPS file and set a limit to your shadow copy storage
http://nerdsknowbest.blogspot.com/2013/01/phantom-space...

You can disable hibernation and delete your hiberfil.sys file http://nerdsknowbest.blogspot.com/2013/01/how-to-delete...