I wanted to check your site - but my browser and Avast said that:
Wait, this site is not secure
We found malicious code on this site that can cause damage to your computer or steal your private data. We recommend you not to open this site at all.
And there is possibility to set different color for each submenu. But request more customization. I am not sure it's still support or typical customization task.
In general you have to use custom Class name for Main menu items then define subcolor bg.
Do you need short video guide?