Customize Wordpress Theme to create 2 similar sites

I need to create 2 simple websites in the RX field. Site#1 will be 1 page and a blog. Site#2 will be 5 or 6 pages and a blog. So these are highly similar sites with different color schemes, images, text and m inor layout differences. I will indicate required colors and design features required and also provide images. I can also direct you to a site to 'clone'. The sites will need to be optimized for speed including W3 Total Cache plugin and other WP best practice for speed (must rate 90+ on google speed tests) Social network plugin and Yeost SEO plugin as wll. I will put up the starter sites and install WP on both sites. Obviously, with such a simple site we can start with one of the standard, simple WP themes and adapt it.