If what functionality should be on a site, it is possible to speak only clearly, in each case, about how bright the site that sells should be said rarely.
The general trend is this: the customer wants YES, so YES. And it does not care that as a result of such a color scheme the customer will lose half of the customers. Sincere respect for the customer is to do as it should, not as he wants, justifying his position. The main purpose of existence of any web resource is commercial. First you need to decide: do we make a site for the customer personally or for his clients? It depends on the quality and the result: will the customer be solely a customer of his own resource, or is he interested in selling to others?
What you like personally, may not like 99% of the planet Earth.
So, how bright should the site be?
- enough not to cause boredom;
- not enough to cause a rainbow page to close without making a purchase;
How do I offset simple monochrome colors on a page? Quality product illustrations, clean code and neat layout.
When there is no taste put on everything bright at once. When it is: Dress only what is comfortable. The times of the gypsy in web design are long gone.