If you want to emphasize professionalism and expertise on your website, use 1 color that takes up 80-90% and 1-2 additional colors as an accent.
This is what we call the "boutique rule", as in luxury stores, things are never crowded on racks in narrow aisles. On the contrary, every item has enough space around it to be noticed.
Similarly, on a website, discreet use of accent color will draw attention to key elements, such as CTA buttons or subscription forms.
When people buy a product or service, they want to be sure they're paying for your expertise or excellent quality. Moderation in the use of colors will maintain their confidence and help them better appreciate your product.