How to test color harmony and accessibility for a wellness brand palette and CTA

[Zoey_L]

I'm a junior graphic designer working on a rebrand for a wellness startup, and I'm struggling with applying color theory for graphic design to create the right mood. The client wants a palette that feels calming and trustworthy but also modern, not clinical. I've started with a base of soft blues and greens, but I'm unsure how to effectively introduce a complementary accent color for calls-to-action without making the scheme feel jarring or unbalanced. What are some practical methods for testing color harmony and ensuring accessibility, and how do you typically present color rationale to clients who might not have a design background?