1) Provide me temporary Dashboard and FTP access to your site to check the saving process.
Main color change the color of the accent elements like active buttons color, sale price color, links active and hover color, blog categories color etc. So, everything depends on what exactly do you want to change. Can you provide me screenshot of the elements?
2) Read this topic about site speed and recommended actions https://www.8theme.com/topic/speed-34s/#post-190330
If you provide me Dashboard access I’ll be able to help you with cache plugin installation and its settings.
