Hi there,
so is it only the home page that will be the different color? If so it may be easier to switch the colors in customizer so all your other pages are correct and then we can provide some CSS to style just the home page. Let me know.
If you want to increase or reduce the size that the image on the single product occupies then:
1. Make sure you have GP Premium up to date ie version 1.8.2.
2. Appearance > GeneratePress – makes sure you have the woocommerce module activated.
3. Then in Customizer > Layout > Woocommerece you can set the Product Image Area Width.